Are first the few Pams which never saw the light, as this special Pam 92, for example:
Don't know who to credit for this pic...
Then among the Pams which were produced....
1st of them, the Pam 208, which is basicaly a Pam 198, but with a brown hobnail dial...
It was made in a LE of 5 pieces, for the 50th of the AD Sincere, but I only know one which was produced, the Nr 1...
So I think that is the harder Pam to get.
Pic courtesy of Y.O.
Then, as mentionned Asi, of course the Pam 77, which was made in only 2 pieces.
And, of course, but if you have the money, it's not a problem to get one, the Pam 21and 203...60 pieces, and 150 pieces each.
Best.
nicolas