Or, I suppose you play in this way:
… But I prefer this:
The first option seems to have worked perfectly.
Probably not if you are working with ordinary running text. It would add a . after the A in any sentence that starts with A, and after any occurrence of I. The second expression is looking for a word that starts with an uppercase on either side of the single uppercase letter, as you would expect to see in a name, and is less likely to give you a false positive match, though it still not foolproof.
Don't forget: Never enough of an apparent solution!