Yeah, I'm surprised. I'd always assumed that people would use the full form on the birth certificate even if the child was never actually called that in practice.

Doesn't really matter, I suppose - names are pretty arbitrary anyway and I can't imagine the sort of pain that would be involved in trying to force-canonicalise Jack->John, Leo->Leonard, Theo->Theodore (or Theobald?). Even the French don't do that any more!