Logging oil changes

As some of you know, I'm in the market for an airplane. To this endeavor, I
find myself reading through a lot of maintenance log books.

I've noticed that some people log oil changes but some do not.

I'm a little worried about the owners who don't because I don't know if the
oil is ever changes or not. (Yes, I know that it just being in the log book
doesn't mean it is actually done, but it does a lot to put my mind to rest.)
All the owners I've talked to claim that they do oil changes in 25 or 50
hour intervals, but they don't log it.

Do you log oil changes?