I know your PBs (plate blocks) are M-NH.
What about the rest of your collection, also M-NH ?
The reason PBs are not as popular as say in the 60s or 70s is that people do not want to spend $$ on PBs ! I have a big collection from my father and intend to keep them.
Each stamp is worth its face value when put on a
Canada Post letter (incl tx!)....but when you want to sell, it is another story.....Chasa's proposal of 50% (US$) seems good to me. Good luck !