I have a customer with a single 90-30 in their plant. It came with the machine. They also got the license for VersaPro along with the machine. The program was written with VersaPro version 1.50. They never purchased a software maintenance contract.
I have version 2.03 on my laptop. If I were to go online with the program using my laptop, I would have to convert the program to v2.03. If I did that, they would no longer be able to upload the program from the PLC to their computer running v1.50. They could still download a v1.50 program from their computer to the PLC, but if I made any changes using v2.03, they'd be out of luck.
I get around it by using their computer as much as possible when I'm onsite at the plant. I make a backup copy on a floppy and convert it to v2.03 on my laptop so I have a current version of their program in case I need to provide phone support. On the rare occasions when I have to go online with my laptop, I uninstall my v2.03 and reinstall v1.50 (I keep the CDs with the earlier versions).