in my opinion they are at mistake while asking you for a HUF Deed since there is no need of any deed to form HUF. Have words with the concerned manager.

There can not be any HUF deed ao no question of dated or back datted. Pl ask the conerned bank to refer the matter to their legal person that under what povision they are asking for HUF dee. The creation of HUF is historic fact and comes in existance by perpetuation., and not by any agreement or deed. If the HUF is created by partial partition than only a partition deed is the originator of a fresh HUF while the original HUF remains in existance also.

HUF cannot be created by agreement, hence you producing a deed does not arise. HUF is status of the family which comes by living a family in joint from bigining and same cannot be created by coming together after severance of joint status.