Multi-tasking

Nicely (actually, nearly pivotallly) I can get some stuff done at my indispensable and WONDERFUL part-time job. Tonight, we're mailing. Non-machinable "Butterfly" stamps ($0.71 each) and slim, security envelopes from Office Depot. It's a bit confusing. I've asked my USPS workers if it's okay to send sports cards, slimly packaged, stamped this way. They say "No". But, they still work. And, why else sell these stamps if not for this? It is best if you limit it to two 55pt to 75pt cards in one or two semi-rigid protectors (not top-loaders).