STCW Question for Mr. Cavo

I have a deckhand (on a Tug) that has taken the required STCW courses but only holds an Ordinary Seaman… on his MMD. He was informed by a REC that they would not issue a STCW certificate until he had a AB or QMED endorsement on his document. Ok I can go along with that. My Question is how do Ordinary Seamen on ship sailing foreign handle this. Aren’t they required to have a STCW certificate?
Secondly, He has various types of sea time on various tonnage vessels. As most sailors do. My question is based on past experience, supposing he turns in sea time for the AB Limited or Unlimited, and still holds sea time as working in the engine room. Does using that sea time for AB use up all the sea time if it is one one letter or combined with his deck time?
Example, Years ago (more than I care to count) I used my sea time letters to upgrade from limited AB to Unlimited. When I went back later with some engine room time and tried to use the extra sea time not need for the upgrade I was informed that this was not possible because I had use that sea time up. Even though I had a few hundred days over the requirement to upgrade.
The first question is the only one that we really need an answer on. The second is just one of those what ifs.

There is no STCW requirement for an OS. You just have to have your STCW basic training to fill the station bill.

The REC is partially correct. We will not issue STCW cwertificates to masriners who only hold entry-level credentails. However, it is not AB or QMED that would lead to a certificate being issued, it’s RFPNW , RFPEW, or Proficiency in Survival Craft. A mariner can get these before they qualify for AB or WQMED.

If mariners need BST but only have entry-level credentials, they need to carry their BST course certificates to prove that have had BST.

Sea time alone won’t qualify someone for RFPNW, they need to complete the assessments.

Bingo, Thank you Mr. Cavo