Built to spec. Not built, not tested, not certified for it’s intended use.
Studying this a bit, it becomes obvious why there wasn’t any certification.
The entire number of deep sea submersibles is less than ten, and all the others are made of titanium.
Alvin is typical. It weighs 17 tons and has two inch walls on the pressure hull.
Titan was the only deep submersible that used carbon fiber, five inches for the pressure hull walls.
Sixty years of experience has taught exactly how many dives a titanium hull stands before it needs rebuilt. Alvin has been rebuilt maybe ten times, so far.
With carbon fiber, they’ve learned however many dives Titan made was too many.
It’s going to be a long time before another carbon fiber pressure hull is built.