Is there a difference +X Damage and Extra/Addition/etc. X Damage?

Is there a difference in game mechanics between +X Damage and Extra/Additional/etc. X Damage?

The skill desciptions are usually worded very particularly I was wondering if there's a difference in game mechanics for the damage skills (ie. Ignores armor, is(or isn't) multiplied on a critical hit.

For instance, at 15 Swordsmanship:
Galrath Slash does +40 Damage
Final Thrust deals 40 More damage
Savage Slash deals 40 extra damage (if it interrupts a spell)
Standing Slash deals +20 damage and an additional 20 if in a stance.

No. There is no difference.

No +damage or extra/additional/etc damage is multiplied on a crit hit. The only thing a crit hit does is multiply the raw weapon damage by 1.41.

Thank you Marty

While additional damage does not receive the crit multiplier, it is always armor-ignoring unless it specifically identifies a damage type. For example, "+40 damage" is armor-ignoring but "+40 slashing damage" is not. There are a few skills (especially for elementalists) that do specify a damage type.

A crit also forces a max roll on your weapon damage. (At least for players. Pets and minions are a different story/)

And to make matters more confusing, some descriptions are not correct. Some skills that specify a type do armor-ignoring damage anyway (Conjures for example), and some skills that don't specify a type have one (and respect armor) anyway. When in doubt, check wiki.

I think the biggest anomaly is Ancestor's rage (A-rage) and Conjures. All the + damage from attacks is armor ignoring.

But some of the damage multipliers are lineair, and are added AFTER everything is added up. Asuran Scan and Vow of Strength come to mind. So, if you hit with you sword, and do 20 damage, +15% from your 15^5, +40 from one of your attack skills, Asuran scan is added AFTER all of that. So you get: (20.1,15 + 40).1,75 = 110,25 damage. Which makes Asuran Scan one of the most imbalanced skills in this entire game. Try combining it with Vow of Strength, but don't forget not to run any conditions. It's gg, you won.

Let's say you run critscythe with 15 Critical strikes 10 Scythe mastery and 9 Earth prayers (attribs might be off, but w/e) And you land a critical hit:
Let's say your scythe does 38 damage, you hit with a Mystic sweep at max enchants, and you have AoHM up at max Luxon/Kurzick.
So: ((((((38.1,41).1,15).1,74)+30).1,35).1,75) = 324 damage (the 1,74 is from AoHM, dunno why, the skill description says 32% more damage, but wiki says it's 74% at r12.. If i'm wrong, please point it out)

With this situation, you can do anywhere between 113 and 344 damage (minimum is 9 damage, no critical hit, maximum is 41 with critical hit) against 60 armor..

The description of AoHM says +xx% damage, but it's actually +xx damage. At max rank it does +32 damage, not +32% damage. (+dmg to effective dmg rating btw)