Lyon was born late in Tyler's life, and he himself became a father late in life. As a result, John Tyler still has a living grandchild at he time of writing despite John Tyler himself being alive in 1790.
There are a few names which are actually variants of each other (Ann - Anna - Anne, for example). If you like the idea, could other versions perhaps automatically fill in when you type in one of them? That would help, but not too much.
You have nicknames accepted for some, and not others. First names are not accepted for a couple and a few spelt wrong.