How do you edit a check number?

We have Netsuite Small Business, and under Bill Payment we wanted to enter the check number, because the check was already written out, but the check field is blanked out, we unchecked to be printed & uncheck bill pay, What am I doing wrong?
I even went under Lists, Accounts, and clicked on the checking account, found the vendor & clicked on edit & I couldn't change the check number there either, why?
I can change the number under Write Checks, so I could void these bills & re-enter them under Write Checks, but it seems like I'm missing something.  If someone could point me in the right direction, I would greatly appreciate it.