[Mahler9th]

There is at least one video interview with Mr. Rush where he states that the design/construction process of the Titan's composite tube included the knowledge that holes in that structure were a no-no. I doubt that the tube had any through-holes.

As stated before, the Nereus design featured a ceramic tube with Ti flanges that were glued on and Ti end caps. But this was an unmanned vessel.

Lots of engineering info on the Nereus in the public domain, included at links I already provided.

I do not know if any design elements and/or construction processes and/or materials (like adhesive) and/or testing of Titan leveraged learnings from the Nereus and/or the DeepFlight Challenger.

But I think it can be helpful to consider the possibilities.