The reason why people would manually adjust kerning is the same reason why it might have been done on a birth certificate. We used to do it so that we could fit more text into blocks on government forms. If you had an extra character or two that wouldn’t fit using normal kerning, you could scrunch it a bit to make it fit. I’m not saying that’s what was done with the Obama birth certificate, but it’s one plausible explanation.
You could also get the same result by hitting the "1/2 backspace" key on some machines, or by manually sliding the paper over, or by not hitting the "space" bar with an even pressure, which could affect how for over the next key struck.
I'll give youngsters the benefit of the doubt, and write it off top ignorance, if they buy this. But as to anyone old enough to have used a real type writer, if you think that 1 overlap is evidence of kerning, you are either lying, or being willfully delusional.
If you want to see what "kerning" looks like, look up Buckethead's post re Dan Rather's fake documents. If you want to see what self delusion look like, look up Dan Rather's comments that his fake documents have never been proven to be fake to his satisfaction.