Am I understanding this:

You have one table with a employee id, and in that id you two possible cases: straight number and number with a TS prefix.

You have some employees who are both in there as a straight number, and as a TS prefix with the same number after the prefix as their employee number.

- OR -

you have some employees who have different numbers, but the same name, and you want to find them, and consolidate them to the straight number and get rid of the other one and set the dtlastlogin to the most recent login date.

Can you also provide a couple of examples of employee numbers that are hits as well as some misses?