Is it true that a 200 Ton Master can be used as a 500 Ton mate? Or is this someone pulling my chain?
No. It can’t. I can’t post a link to something that doesn’t exist, but look at 46 CFR 15.900 et seq. and note that there’s nothing like it there.
This is strictly conjecture, but this twisted notion could have come from someone formerly having a 200 grt master (500 ITC) license. Who knows.
If you had a 200 GRT masters back in the day with STCW, you were granted 500 GT (ITC). The STCW was BST and II/3. That’s master 500GT OICNW. Now that requires the schools. As for your direct question, I don’t believe so.