They have the data but the numbers restarted at 1 and search in the new system isn't good. I think they all agree the old system was better - but the new license terms were unacceptable so we left anyway.
Restarting at 1 makes sense only if you think you’re going to run out of integers.
I can’t fathom why part of the deployment of the new system wasn’t to re-seed to the current ticket number or an easy-to-remember integer (hopefully via database, but also ok even if via a Selenium for loop to pull 19,999 tickets to burn the numbers in the new system).
Different systems have different ways of working. some have one number some start at 1 for different types of tickets. A bug and a new feature have a number of differences.
The data in the ticket system should be considered important as it's the primary interface through which developers, QA and design share information.