Which aircraft are 76A, 76B, 77E, 77F?
These are mostly IATA type designators, except for OAAG, 76A, 76B and 77E.

77F is the official IATA designation of the freighter version of the 777.

The rest:

77E seems to be an internal designation used by British Airways for a specific sub-fleet with an increased gross weight.

76B seems same as above just for 767-300ER.

I wasn't able to find anything about 76A (but I'd guess that same as above) and OAAG (perhaps it is part of the registration of an individual aircraft)