Technically, I don't think there's anything that adjusts THAC0 (other than level/HD). Everything else is expressed as a bonus/penalty to the attack roll.
Now, on the sheets I made myself for 2e, I remember having spaces for adjusted THAC0 for melee, ranged, and thrown attacks (adjusted for Strength, Dexterity, and both), and the weapon table on the sheet also had an adjusted THAC0 (which would also include things like weapon specialization and magic weapons). But that was a convenience I created for my players, not something official. Technically, a 6th level fighter with Strength 18/00, a +2 weapon, and weapon specialization would still have THAC0 15 for being a 6th level fighter, and then add +6 to attack rolls. On my sheet there'd be an adjusted THAC0 of 9, but that wasn't official.
What is more confusing is AC. Let's say you wear chain mail for AC 5. You have Dexterity 16 which gives you a Defensive Adjustment of -2, which you apply to your AC, lowering it to 3. Then you find a ring of protection +1 – now what happens to your AC? Do you apply the +1, increasing it to 4 (is it a cursed ring?)? Or do you decrease AC by 1 to 2? And if so, why are you using the Dex adjustment straight but reverse the ring's adjustment?