Sounds interesting, i'll have to check my referance books when i get back to Brisbane to morrow night.
As to the promo stamp? Sometimes dealers do that themselves to increase the value, as my old boss used to with many items. This way customers would think they were getting a RARE issue, when thay were only getting a standard issue.
I'd suspect it may be rare, though i'd need a catologue number to find out more.
It's damn hard when you dont have any research material with you :(
Keep on swinging