What else are you going to get over 25 generations?
A probable ancestor of mine has the right parents in 1 RootsWeb tree and the wrong parents in 2 dozen. And counting, because newbies go with the majority. Two men, same name, same sort of age, same area, 5th cousins.
Only a matter of time before he's on here with wrong parents Confirmed by DNA.
American scenario - two people think they descend from different immigrants and the lines join up way back. They match. Confirmed. Actually they match a bit too well, because they both descend from the same immigrant.
You can't even confirm the immigrant without testing descendants of all the candidates, which you can't because too many are unrecorded. We have loads of lines attached to the wrong early immigrant, just because he's there and theirs isn't. If you call them Uncertain, they'll become certain. You can't say "DNA could prove this" and then say it doesn't after you've got a match. You have to know what the match will or won't prove.