no big difference between user names

[symptome]

The members of my board which write a large amount of posts, have a problem with user names that are used more often ... like james1, james2, jamesA, jamesB.
In the end, they aren't sure, what they've written to them in the past, because they can't remember and have to read all history again.

Do you have solutions for that, probably in the process of registration (while chosing the user name)?

Thanks a lot!
Marcel