Note: Labyrinth Lord is not a true Retroclone. It's a really close pseudoclone, but has mixed and matched bits from both Moldvay/Cook and Mentzer D&D. The progressions, however, of several items do not match Moldvay basic, Cook Expert, nor Mentzer Basic/Expert/Companion, namely: save tables, to hit tables, thief skills table.
Few games actually give details past level 20. Generally, tho', one can extrapolate the progressions.
Note that all save tables for humans end where shown; Cleric and Thief at 17+, Fighter and MU 19+, and the To Hits end at the 19+ level line for fighters, the 21+ line for Clerics and Theives, and 24+ for MU, but could easily be extended if you feel it worth doing. Clerical progression on turning caps at 14th level. Cleric and MU spell tables cap at 20th level; the cleric does not match Moldvay, Cook, nor Mentzer. Thief skills also cap at 14th level, save for the bonus of 5% per 5 levels difference in level.
The fighter above 20th is +120,000XP, +2 HP, and the bonus attacks to level 25; no further gains of to hit nor saves.
So, extending the table:
1,560,001 20 +22 hp only 3 attacks per round
1,680,001 21 +24 hp only
1,800,001 22 +26 hp only
1,920,001 23 +28 hp only
2,040,001 24 +30 hp only
2,160,001 25 +32 hp only 4 attacks per round (maximum)
Clerics are +100,000xp, +1hp, max out their to hit at 21st level, and no other gains per level, aside from ability to ignore certain spells of lower level casters.
Thieves are also 120,000xp per level past 20, +2 hp each level, and no gains in to hit past 21st level.
Magic Users are 150,000xp per level past 20th, +1 HP per level, no gains in to hit past 24th level, no gains to saves.