Hmmm my experience is a bit different.
I opened my AIB account as a student, and didn't specify a work number at the time. In spite of this I was often asked to enter a work number when signing in to online banking. I always just fill it with any old number, hoping that the next time around I'll be asked for my home or credit card number. Sometimes I'm repeatedly asked for a work number, which is a bit annoying, but I've never been locked out.
A couple of years ago I even added my work number to my account, but it's still not accepted by the online banking site.