The description on page 199 states they attack with “great barbed darts (treat as javelins with +3 to the attack throw)”. Is this a bonus to the troglodytes’ attack with the darts, or a penalty applied due to the potential unwieldy nature of the dart (so a trog with an attack throw of 9+, for instance, would have an attack throw of 12+ with the dart)?
IANAA, but based on the AD&D Monster Manual, it should be a +3 bonus to the die roll (in the MM, it’s written as “Their javelins are great vaned darts which have a +3 chance to hit when used by troglodytes and cause 2-8 hit points damage.”).
The Dark is correct. Troglodytes get +3 bonus to the die roll.
Well, I made a mistake in my player’s favor, then 
If I were uncertain, I’d have done the same. Better to err on the side of humanity!