Can land be sold without Mutation ?

Hi , i am planning to buy a plot of land in Kolkata, West Bengal from the land developers. The developers have bought the land plot from the owners and also have the documents to prove the same. But the developers have not got the Mutation in their name and its in the name of the original owners only from whom the land developers have bought the land .When i asked why they (developers ) have not mutated the land in their name , they said wit will incur huge cost and thus they will directly change the mutation from original owners name to my name, in case i go for registration. here , i want to know whether thjey can sell the land , even when they dont have mutation in their name ?? Also if i go for the purchase, i will buy the land from land developers but will have mutation exchanged from original owners , can this lead to any complication later when i want to further sell the land?? please guide whether i should go for purchase or not and what things i should insist upon ?? Thanks in advance