Here is one way you can get into trouble if your account does not have your current plate number on file.
In July, we drove from Boston to Philadelphia and back, encountering tolls in MA, NY, and NJ. On the way home, in NJ I noticed that we got the yellow light and a message saying the toll was not collected, on the Garden State Parkway. I was not sure what to make of that. When I got home, I checked my EasyPass account online and realized that some of the tolls we had incurred were not listed. The reason was that the battery in my transponder had died. Not too long after that, I got bills from NJ for tolls not collected along with a large fine or fee -- I think it was either $25 or $50 for each of two tolls. They had read my plate and billed through the mail, because the transponder was dead AND because my EasyPass account did not have my current license plate number.
I immediately corrected my oversight and listed my plate in the account. After i got the NJ bills, I called the office in NJ and explained i di have an EasyPass account but had the wrong plate listed. They told me to file a form saying that (it came with the bill), and to pay only the toll, not the fine. Nice!
I also incurred tolls in NY, but apparently they were slow enough to bill that when they queried the MA database, they saw my EasyPass account with the corrected plate number, and all I had to pay was the tolls.
The transponder battery lasted several years (five or more), so this combination of events would not happen often. But even if the transponder is not read correctly for some other reason (rain, snow, bad signal, etc.), the collecting agency would query the MA database so a current plate avoids issues and fines.