Check the Sale Permission document as well as Sy.No and other documents with respect to that SC/ST Land. Also confirm and verify before the A.C office, since some builders will create duplicate sale permission and other documents. It's advisable to buy plots in any other Sy.No other than this SC/ST land. For other Sy.No's ask to produce PTCL endorsements.
A local expertise advocate may be approached for the opinions to be given on scrutiny of all the relevant documents/ papers so that you do not get trapped with improper suggestions and opinions had it otherwise.