Is this on all UA operated flights? Or does it involve other airlines?

Generally once ticketed, names (including misspellings) can not be changed. If it is all UA, a senior supervisor can fix this. If any partners, no way.

However, it is hard to know where the error was made and after the 24 hour period where there was a chance to review the tickets, this becomes a very difficult issue.

The issue can be a check-in problem and a security checkpoint / immigration issue. A note in the record can handle the first. The second may or may not be an issue especially if it is a common variation on a name.