Thief skills in old-school D&D have always suffered because no clear guidelines were ever established as to how to really handle them. The skill titles were suggestive of near-supernatural or special ability but it was never spelled out. This left it to referees to adjudicate them as they saw fit.
For thief players, this meant that their play experience could vary greatly from table to table and referee to referee. As a referee, the lack of clear guidance meant that we couldn't be sure how it was meant to be. Of course, we would create our own version of the class, in a sense, but it always had the potential to leave a niggling doubt in our minds: are we doing this the right way?
Thus, the question of what thief skills mean and how to run them has been a near-constant topic of conversation from time immemorial up to the present day. I am sure that I am not adding much new to this but it was new to me so I decided, for the sake of history, if nothing else, to share this little nugget that I unearthed from module X2, "The Isle of Dread".
In area 13 of the island, there is the Aerie of the Gargoyles. Within the description of this section is a note about climbing the cliff to reach the gargoyles' nest:
For our purposes, the relevant text (highlighted in the image above), reads:
Any non-thief character who tries to climb the cliff must roll less than his or her Dexterity (on a 20-sided die) or fall to the ground. The fall will cause 3-18 points of damage. A thief will succeed automatically in an attempt to reach the lair.
What's the big deal, you may ask? Well, here's a clear example of thieves being exempted from a skill check because of their class ability, namely Climb Sheer/Steep Surfaces. Climbing a cliffside isn't exactly a walk in the park and many referees, without this note, might certainly feel it appropriate for thieves to roll (and, frankly, with an 87% chance at first level, it's not exactly a hardship) but that's not the guidance. Instead, they get to climb up without a roll at all while everyone else gets to try a roll-under-attribute test.
The entire scenario at the aerie reinforces a mutually beneficial relationship between the thief and the rest of the party. The adventurers approach the cliff and provoke the gargoyles. During that fight, the thief is going to be of very limited assistance. However, assuming the gargoyles are defeated or driven off, the cliff presents a lethal challenge for the non-thieves. Sure, with a decent Dexterity score, you've got a potentially good chance of making the climb, but any failures are almost guaranteed to be lethal. Do you want to take that risk? Iffy. But, look here, the thief can do it without any risk to themselves. They can go up and examine the nest while the rest of the gang holds down the perimeter from the ground. Win, win.
I know that I'm not alone in delighting in finding these half-hidden nuggets of wisdom sprinkled throughout old-school gaming books. My only wish is that they had been collected and presented in the core books in some sort of organized fashion. These tidbits help shed light on how the game was run and played by the folks making it. While that may not be the end-all, be-all, a lot of thief characters may have benefited if this information like this was more widely known.