I think you are probably right, I do have a very small collection of aluminium tins and trying to date them can be very difficult, I do have an A571 mk1 with a Label with a packing date of 03/01 (believe Re-pack) and an A610 Mk3 base marking and on the body an original ROF Chorley label filling date 08/04, this tin could have been sat around for some time before being used??. I also have a few tins that do not have any marking at all, some do have filling/packing labels Dating form the 90's through to the last couple of years, and of course they do get re-used, I do like the small Containers and accessories that some may ignore, The Containers I have, have varying amounts of the original internal packing.
Richard