DaasYochid:
“Any time one drinks from a kos, the remaining wine is pagum”
What is your source for this comment? It doesn’t make sense that while drinking from your own cup (some times it may even be a kos shel brocho-birchas hamozon) it would change into a status of “pogum”.
I would rather say, while in this original cup IT IS NEVER POGUM, pogum only becomes once it is out of the original cup – unless more gets added.