2 Years of skipped patches, updates, and basic maintenance skipped at an accounting firm with just over 100 PCs is the worst I've seen. Most the Windows 7 computers had never had updates run, ever. Same with a bunch of the 2008 servers. The Exchange server had one patch level, maybe.
Everything worked, somehow, and of all things backups worked. I do feel sorry for the previous tech, the company had become so change averse that he was hamstrung by the fear something may go wrong that he had stopped doing any updates. Unfortunately this built up a huge maintenance debt and things started going wrong and he couldn't keep up, and they fired him because he didn't do his job.
They had another firm come in for a few weeks, and I assum told them they needed to change the way they did everything, and that, yes downtime had to occur. They got rid of them and I ended up on the project. Told them the same thing, this time it clicked and they figured out there was some kind of structure problem. Worked quite a few weekends since then getting everything caught up.