You need to file civil suit to challenge the same the documents needed js the sale deed if any done which you need challenge 

Your case is not one of regularization, but primarily of wrongful reclassification and protection of bona fide purchasers. The fact that the land was registered on the basis of an official certification by the Mandal Revenue Officer (MRO) is a very significant factor in your favour.

Your queries are addressed as under:

1. The correct legal characterization of your case is correction of erroneous revenue entries along with protection of vested rights of bona fide purchasers. Since the sale deeds were registered based on an official MRO certification and possession has continued for over two decades, the State cannot lightly disregard such vested rights.
2. The earlier MRO certificate issued to the Sub-Registrar has strong evidentiary value, even if presently available only as a scanned copy. It constitutes an official act of a public authority and can be relied upon. However, it is advisable to obtain a certified copy or secondary proof (through RTI or from Sub-Registrar records) to strengthen your case.
3. Authorities cannot arbitrarily ignore earlier official certification and unilaterally treat the land as Government land without due process, inquiry, and notice to affected parties. Any such action would be vulnerable to challenge as arbitrary and violative of principles of natural justice.
4. The appropriate first step is to approach the revenue authorities (Tahsildar/RDO/Collector) by filing a detailed representation seeking:
   correction of Webland/revenue entries,
   recognition of patta status, and
   initiation of formal inquiry into the discrepancy.

This step is important both procedurally and strategically.

1. If the authorities fail to act, or if there is any threat of coercive action such as eviction, you can approach the High Court by way of a writ petition under Article 226 of the Constitution of India, seeking:
   protection from dispossession,
   direction for proper inquiry, and
   correction of records.

Courts generally grant protection where long possession and official acts are involved.

1. Coercive action or eviction without adjudication can be challenged immediately, and courts usually grant interim protection until the dispute is properly examined.
2. A civil suit is also an option for declaration of title; however, given the nature of the issue (revenue classification and State action), a writ remedy is often more effective and faster at the initial stage, especially to secure protection.
3. To strengthen your case, you should collect and compile:
   original registered sale deeds,
   any link documents/earlier title chain,
   certified copy of the MRO certificate (through RTI or Sub-Registrar office),
   encumbrance certificates,
   pahani/adangal/revenue records over the years,
   tax receipts, electricity or possession-related documents,
   any layout approvals or related correspondence (if applicable).

In conclusion, your case is legally strong on the grounds of legitimate expectation, official representation, and long possession. The immediate strategy should be to initiate proceedings before revenue authorities and, if necessary, promptly approach the High Court to protect possession and seek correction of records.

1) The entry of "Anadeenam" (Government land) is a clerical or factual error if the land was already certified as Patta

2) You acted on an official certificate from a competent authority (the MRO) to purchase the land.

3) The High Court has held that revenue authorities cannot "unsettle" land records that have remained undisturbed for decades, even if no limitation period is specified

4) file writ petition in HC for correction of wrong revenue classification 

5) old MRO certificate has evidentiary value 

Anadeenam refers to land that is "unoccupied" or "vested in the Government" due to a lack of clear title or a break in the chain of succession.

The fact that an MRO (Tahsildar) issued a "NOC" or "Clearance Certificate" in 2006 for registration is your strongest legal leverage. The government cannot unilaterally change the classification of land from "Patta" to "Anadeenam" without a detailed inquiry and notice to the affected parties, especially when it was previously cleared for registration

You can submit an application to the authorities concerned  for correction of wrong revenue classification (re-entry of the land from Anadeenam to Patta).

While a certified copy is preferred, a clear scanned copy is secondary evidence. Under the Indian Evidence Act, you can file an application to lead secondary evidence if you can show the original is in the possession of the Sub-Registrar (SRO) or Tahsildar and they are not producing it.  The SRO records usually contain a copy of the letters they receive from the MRO.

You can file an RTI (Right to Information) request or a "Search" application at the SRO to locate the original entry in their "Correspondence Register" or "NOC Register" for the year 2006.

In various judgments (e.g., G. Satyanarayana v. State of Andhra Pradesh), the High Court has held that once land is treated as Patta and registrations are permitted, the revenue authorities cannot suddenly include them in "Prohibited Lists" (Section 22-A) or change them to Anadeenam without a fresh, valid reason and a prior hearing, hence the authorities cannot ignore the old certificate.

The government must issue a Section 7 Notice (Show Cause) under the AP Land Encroachment Act, 1905,before taking possession. You can use the 2006 MRO certificate to show that your possession is not "encroachment" but based on a valid title cleared by their own department and challenge the eviction. 

You can check the "Pattadar" column in the original RSR (usually from the 1920s/30s). If it was Patta then, the Anadeenam entry is likely a clerical error during digitalization. Collect manual Adangals from the period between 1980 and 2006 showing the ryots' names. An EC showing the 2006 transaction and the lack of any "Government" claim at that time. You can ink documents viz.,  prior sale deeds that the ryots held before selling to you. and secure the tax Receipts: Evidence of payment of Land Revenue (Kist) or Property Tax by the purchasers.

You can approach the high court, if necessary  with a writ petition and stay application for legal remedy and relief.

The government, no doubt, has every legal right to reclaim its encroached land, notwithstanding any claim of adverse possession by continuous occupation and enjoyment over a long period of time. In your case, the MRO's certificate will not be of much help in evidence; more so when you say that the original is not available. There is no harm in trying to appeal to the Revenue authorities such as the Tehsildar and the District Collector. If your request is not favourably considered, it is better to accept any reasonable compensation than pursuing any legal action than, as the chances of success appear to be rather bleak. 

This is mainly a case of correction of wrong revenue record, not regularization, because the buyers purchased by registered deeds after an official MRO communication showing the land as patta; first move the Tahsildar, then RDO appeal, then Collector revision.

The old MRO letter does have supporting value, but a certified copy from the Sub-Registrar/Tahsildar record is much stronger; collect old 1-B/Adangal/FMB and possession-tax records also.

They should not treat it as government land and evict you without proper notice and inquiry; if coercive action starts, a writ for protection is maintainable, and if title is seriously disputed, a civil suit for declaration/injunction may also be needed.