Nah, no crawling back, you said Titanic's was best, and that nothing beats. So you thought that it was a steam sound.. And why would you not, it's not thát much different. Steam will have a different density and the temperature will make a difference, but unltimately I think it's more about the whistle itself, not the steam or air. So the tone and volume and 'body' may very a bit, but a good whistle will probably sound good either way.
But since none of us here have ever heard her for real, and you can thus also not make that distinction, it's close enough for me, this way. That's why there's no replacement for Titanic's horn in the addon pack. Terry and I agreed that it was good enough, since it is the real deal.
So yep, the original whistle, that they recovered and refurbished, and used that time, that sound is the one that is sampled in the game, to the best of my knowledge.