Thieves and Traps

"One of the interesting peculiarities about the Supplement I (and Holmes) thief class is that, while it possesses a "remove traps" ability, it does not possess a "find traps" ability, which wasn't introduced until the AD&D Players Handbook and also adopted by the Moldvay rules. (As an aside, it's worth noting that the Cook/Marsh Expert Rulebook lists only "remove traps" as a thief ability on its class tables, although one presumes this is just an editorial glitch). I surmise that the thief lacked an explicit "find traps" ability, since it was simply assumed they had the same chance to find them while searching as any other character class (1 in 6). Thus, thieves were adept only at overcoming traps once found but lacked any special skill in finding them."

From Grognardia