Can a STCW / VPDSD certification be revoked by a training program if it is already issued by the Coast Guard?

Maybe. But you would have to report the circumstances of why the school was sent the sticker and they won’t give it to you. You might also be able to apply for a duplicate/replacement MMC that would include the endorsement. See 46 CFR 10.229.There would be fees for this as the replacement isn’t occasioned by one of the events that allow a no fee replacement.

Well, I mean, it’s obviously the SIU, a totally upfront and straightforward union with it’s heart in Sicily. That’s just their thing. You know, their ‘cosa nostra’ as they like to say. Every union only has guys whose name ends in a vowel as their officers, right?
Asking the SIU to not act like legbreakers and grifters is like asking the dog not to lift his leg on a tree.
The scorpion and the frog called.