I like those old tins too.
I've read that PA was still available in pocket tins as late as 1985, complete with a barcode.
RJR sold the PA brand to John Middleton in 1987 and packaging changes occurred then too.
One source for finding good info is the Legacy Library. I went looking but didn't find anything about an official discontinuation of the pocket tins, but it's a vast swath of results to search thru and requires much patience, i usually only search thru the BAT archives for British info as it's easier to find...
...but what about this?
Dear Sir, there's a hair in my tobacco!
http://legacy.library.ucsf.edu/action/document/page?tid=mol93i00
...or this document, Capt.Black has 18% PG & highest nic of the listed brands, Edgeworth is the 2nd lowest in nic! etc etc
http://legacy.library.ucsf.edu/action/document/page?tid=bpm20d00&page=2
The curved pocket tins are cool too, like this one:
Here's a book with some good stuff, including old tins of SG Skiff 7 Grousemoor,
http://books.google.com/books?id=jSAxX7r3dQUC&printsec=frontcover#v=onepage&q&f=false
A good selection of various pocket tins can be seen here:
http://antiquetobacco.com/tobacco-tins/pocket-tins/
All that beautiful lithography would cost a fortune nowadays!