Society cannot claim unsold parking spaces till conveyance deed is executed in favour of society 

Once the society is formed all common areas belong to society even before conveyance. If the parking space is garage as per rera then only builder has right to sell the same otherwise no

As per the sale agreements you have to allot 1 parking to each Apartment holder without the parking space you cannot sell the apartment and even after the sale of the entire flats if there is any an allotted parking space in the society then society will have right on the property and you will have no right to society cannot sell the rights of the parking to any individual but it can use parking for the parking lots of the residents are otherwise can rent parking

1. During the Handover process, you could have given a List of Flats and linked parking spaces to the Flat.  IF yes, THEN issue the Society a Legal Notice that the Four Stilt spaces are linked to the Four unsold Flats and would be allotted according on sale of the Flats.  Based on the above, the Society will not be able to claim the "4 stilt parking spaces linked to the 4 Flats", since it would amount to breach of trust and contract/agreement, which you earlier executed for other 100 Flats on the same terms & conditions.

  You can prefer to coordinate with me, IF interested to have a regular legal advisor for your routine issues.

Open parking cannot be sold or retain unless not allotted. Once society is formed, land and common area belongs to society. 

But when ever flats will sold, buyer will get the right to use parking.

builder becomes the automatic member of the society as during registration of society. The appendix submitted shows as unsold (in his possession). Hence, the builder has to pay the maintenance.if builder paying regular maintenance for unsold flats then society cannot claims builder unsold flat parking space .

The society once formed will take possession of all common areas,

The car parking space is one among the common areas. 

 However, Conveyance deed is a final document which a builder has to give while transferring the ownership of land on which a housing society building exists in favour of the society. 

Conveyance is a Transfer the Title of Land and Building by the Promoter/Landowner in favour of Housing Society by execution of Conveyance Deed., hence it is important for the society.

As per the housing society bye laws, the main objective of the formation of society is to obtain conveyance and if the conveyance is not executed by the promoter/landowner within four months of the registration of the society, a case can be filed agaisnt the landowner/promoter to obtain the conveyance.

As per section 13 of MOFA, 1963, failure to give conveyance is an offence and the promoter/landowner can be imprisoned up to 3 years or fined or with both. 

1. No society cannot claim parking for unsold flats.

2. Society have to allot parking for unsold flats as its duty and responsibility of society to allot parking space.