Anyone holding a dde license can get issued to them chief osv with no further testing. There were allowances for getting assistant engineer osv unlimited hp as well, which would help with someone stuck with limited hp. I think that changes after march 2019.
Chief and assistant osv no longer have tonnage limitations.
From what you have described, unless I am mistaken, sounds like you may hold chief engineer limited near coastal. If that’s the case you could get chief limited oceans 1600 grt with just asking for it because the near coastal license has been removed.
The only other caveat to your particular question would be is there a tonnage limitation on the int’l side of the license. I mention this because of the GT you used…which makes me ask does the OSV have dual tonnage?
DDEs cannot serve on ANY vessel over 500 GRT, including OSVs. Even if this is not a DDE license, it says it’s limited to 500 GRT. So it’s not vaild on a vessel over that, regardless of what type of vessel it is. Note that oin the recent past, the NMC was noting “GRT” as gross tons (domestic)" on MMC endorsements.