I'd say the numbers are excessive. One good thing about Ars Magica 5th edition is that it tries to make NPCs, particularly "anonymous ones" rather average, so that focused PCs can outshine them.
The say I see it, a Knight should have:
- Combat Ability 5 (which is consistent with age <30, and with the leader's Leadership being 5, too - for a Group bonus of +15)
- Dexterity +1 (which, together with Single Weapon 5 or Great Weapon 5, means his Labour Point total is at a "break even point" of 6)
- Unexceptional weapons, so the Atk/Dfn bonus for Lance+Heater Shield are 4/3, and for Longsword+Heater Shield 4/4.
Considering that the Knights are mounted (with Ride 3+), their stats should then be:
Lance:
Atk: 4 (Weapon) + 3 (Mounted) + 5 (Combat Ability) + 1 (Dexterity) = 13
Def: 3 (Weapon) + 3 (Mounted) + 5 (Combat Ability) + 1 (Dexterity) = 12
Longsword:
Atk: 4 (Weapon) + 3 (Mounted) + 5 (Combat Ability) + 1 (Dexterity) = 13
Def: 4 (Weapon) + 3 (Mounted) + 5 (Combat Ability) + 1 (Dexterity) = 13
A specialty in Lance could boost the Lance totals to 14/13, meaning all numbers are exactly 3 short of the what's in the book. But all the table seems to be off here and there; for example, the Init bonuses are a tad off. I'll just add that I'd assume Sergeants to have a Combat Ability 4 (consistent with the Group bonus of 12) and the appropriate stats +1; levies a Combat Ability 3 (Group bonus 9) and the appropriate stats 0.