Learned Mr. Vasudevan has rightly advised that all documents have to be acknowledged.
Bank staff tells all customers to drop it in drop box and gives the acknowledgment to all customers who ask for it and if denied insist for it. RBI has issued clear instructions to issue acknowledgment as and when asked for. If the counter clerk declines, obtain it from BM and if you face any difficulty please complain to Nodal Officer, MD of the bank, with a copy to RBI.
All pensioners in the bank may unite and issue notice to the bank. Bank is handling pension accounts for business interest and not for charity.
Bank maintains record/register of all instruments collected from drop box and since bank has submitted it to epf authorities ask the bank to supply the copy of docs submitted by them and acknowledgment obtained by them. If bank declines, you can use RTI route.
EPF authorities shall not easily accept that they have lost the docs. You must be firm at the first place i.e. bank.