SPECIAL RULES FOR DWARVES, ELVES AND HOBBITS WHO WISH TO BE THIEVES
Dwarf: +5% Open Lock, +15% Remove Trap, +5% Move Silently, +5% Hide in Shadows
Elf: +5% Pick Pocket, +10% Move Silently, +15% Hide in Shadows
Hobbit: +10% Open Lock, +5% Remove Trap, +5% Pick Pocket, +10% Move Silently, +10% Hide in Shadows, Hear Noise +1
These are from the Greyhawk OD&D supplement, and are presumably the "special rules" found in OD&D that Holmes referred to in the Holmes manuscript.
Human thieves can specialize, raising a skill by lowering another by an equal amount, to a minimum of 5%. This can be done with each of the five skills that increase each level other than Climb Walls and Hear Noise. Thus, a specialist has 50 percentage points (50%) that can be adjusted at first level.
These are some specialists that are possible at first level:
Picklock: 55% Open Lock
Disarmist: 55% Remove Trap
Filcher: 55% Pick Pocket
Sneak: 55% Move Silently
Skulker: 55% Hide in Shadows
By maxing these out, the other four skills will be at only 5% each (not including Climb Walls and Hear Noise). Many other combinations are possible, e.g. 35% Open Lock, 25% Remove Trap, 5% other skills
At levels 2-6, a thief gets 25 more points per level to be distributed among the five skills,
At levels 7-8, a thief gets 35 more points per level
At levels 9-11, a thief get 50 more points per level
At levels 12 and up, a thief gets more 25 points per level
This option inspired by similar rules in 2E AD&D. The total points for first level and higher levels matches the progression found in the Greyhawk Supplement.
As the prime requisite of thieves is dexterity, it will affect their abilities as follows:
Dexterity of 15 or more: add 10% to each thief skill except hear noise
Dexterity of 13-14: add 5%
Dexterity of 9-12: no bonus
Dexterity of 7-8: subtract 10%
Dexterity of 6 or less: subtract 20%
These value of these bonuses and the Dex ranges are the same as the prime requisite XP bonuses on page 6 of Holmes. The idea is inspired by Gary's OD&D houserules, which mention a bonus for a Thief skill based on Dex, and the more complicated Dex modifiers in 1E AD&D.