Hi Kim, as far as I know although there may be some back end patching that isn't contained in a solution or other updates/fixes pushed to every organisation. You may want to check that with Microsoft, but I've used the Solution History to check the times MSFT were doing updates and they all coincided with a lot of workflow failures we had once so I was able to go to them with that evidence when I created a ticket and they confirmed it was down to them.
Regards
Paul