This meta-question is similar to one already asked. But the older meta-question mentions the case of an answer only found in comments. I'm asking in the case of an answer actually posted, and when the OP clearly states in a comment that this answer is correct.
But just as almost happened to me recently, the OP forgets to check the correct place (or does not know how). And disappears.
Wouldn't it be a good idea to consider the answer as accepted ?
I am referring, in particular, to this question :
Which has been considered as a duplicate since yesterday, because I did accept the answer to my own question about one book of the same series. But the OP commented years ago that the answer (namely, the Dr Dillingham's series by Piers Anthony) was correct.