In Harry’s case it is the name his father bestowed upon him, not a birth certificate or other official document, or even what his friends call him now. It is the core of his identity.
With Marcone it may be similar, we see no family but it is what they would have called him.
Harry has picked up on this I think, his use of “John” in dealing with Marcone may be the truth, and that needles Marcone his real first name is likely John not Jonny or Johnnie (both of which are used in the files, and yes I think that is deliberate) it’s his last name which is assumed. Marcone is an Italian patronymic, I do not think Marcone is actually of Italian descent, but his father may have been named Mark or Marcus, and may have been from a military family as he is considered to have had military training. Navy given the “boaters tan” oft referred to.
I think the Tiger Soul is significant, and it is important, Harry only knows this as part of a Soulgaze. The only US military unit John could have served in given his age and associated with Tigers would be Attack Squadron 65 (VA-65), nicknamed The World Famous Fighting Tigers, which was disestablished in 1993, seven years before Storm Front.
Enough info for Harry to find Marcone’s true name?