If the tins have been carefully stored, and their seals intact, LUCKY lucky you--although you almost certain mean "My Mixture 965."
One can assume there must once have been a "365," but its formula would in all probability date from Dunhill's very first years in business--1905-1910 (when 965 was initially introduced), and if Dunhill did still have a customer who liked it in the 1970s or after, your tins would almost certainly come from the London Duke Street "hand blend" counter, and have labelling that makes that fact fairly clear.
A few pictures would obviously settle these matters (and make it possible to date your tins reasonably accurately).
In the meantime, to ascertain the likely condition of the tobacco within, shake them and weigh them--tobacco that's dried out because of a rusty pinhole, will weigh less.