Without being familiar with the specific practice, "past practice" cases are always a massive pain in the ass. If you're defending maintaining a practice, you have to get notarized statements from people detailing when/how long it has been that way, etc. Think of something that goes on in your center that's not explicitly set in the contract, but has "always been that way." Now think of UPS trying to change it over night and the uphill fight it would be to prove it has "always been that way" without it being written down..