No, there was no "C" service in 99 yet, only A and B service. As I said, they didn't go beyond A and B until just recently, 2003 SL and E class cars (the new body styles).
The 90,000 would be the same as a 30,000. The 30,000 is pretty involved. There is a little more to do on the 60,000 compared to a 30,000.
But on the service at 90,000, you'd be looking at spark plugs, transmission fluid and filter, oil change, that'd be the major replacement items. The brake fluid is due to be flushed every 2 years and the coolant every 3 years. It's based on time, so I can't say if they would have done those or not.
Lots of stuff is supposed to be checked, but the owner needs to say yes or no on if some of this stuff gets done or not. For example the service would include CHECKING the brake pads and rotors, but if they are found to be worn out, they would need to ask the owner if they actually can proceed with the extra work.
The engine air filter and fuel filter get replaced every 60,000, so wouldn't be done on a 90,000 service.
There's lots of little items that get attended to on the service, I hate to gloss over things too much like this. Some examples are lubing the door hinges and latches, checking all the lights, rotate tires, check tire pressures including the spare tire, lube the sunroof, clean the tape deck and antenna, lots of stuff like this. It's really up to the tech to make sure everything gets done, need a good tech to do the work, someone who cares about the work.