I have a completely solid grasp of the monk surprise table. That doesn't tell me how it interacts with a ranger's increased ability to surprise; or how many segments a monk is surprised for on various rolls. I can extrapolate in both cases, but I have to extrapolate.Taking each rule in AD&D on their own, I think they're well thought out and mathematically sound. The issue is trying to put them all into play at once, especially if you don't have a solid grasp on them.
Why is a ranger's stealth expressed as a level-independent adjustment to the chance to surprise, while a thief's is expressed as a level-dependent chance to move silently, which is not then linked to the surprise rules? There's no good reason.
How likely a thief is to surprise some goblins if the thief approaches them while moving silently? I don't know. Should it be the same as a ranger? Better? The rules don't say.
As I said, it's a shambles.