I did find a Black Seal explanation on Google
Also, the PVD cases which were used during the Pre-V period, were not "reserved" for special editions, after the sale. They just were used and never re-ordered again (from the same supplier presumably) Some of the Pre-A models, 4 and 9, have Pre-V or 6500 cases, while others have the "new" 6502. The A models have 6502 cases. The PAM26A has a 6502 case. The PAM26K has a DCL case. Like most of the modern "blackies".



Ciao