I just found another distinctive line: vinyl LP sleeves. First I thought all of them were TB, even those published by german record companies. But then I discovered some sleeves from VEB Deutsche Schallplatten/Amiga
, the East-german state music publisher from cold war times, and they are BT oriented.
I can't say anything about the time after 1989, because incedentally that was the year I bought a CD player, and all Amiga CDs I own were published only after the aquisition of the company by West-german BMG in 1994. They are TB, like all the others.