Do masteries apply to every version of a spell?
Say someone gets Demon's Eternal Oblivion (DEO) at level 5 and gets 3 levels of mastery, fast cast, penetration, and multicast. A bit later on the magi has improved Perdo Vim somewhat, and wants a level 10, or maybe even a level 15 version.
Does the mastery for the level 5 DEO apply to the new DEO/s.
Similar question with Aegis.
Take a look at the Mastery Adaptive Casting (HoH:TL p.99). 
No, it dont. But somewhere was a mastery, which allow exactly that - to use it your mastery on the same spells with other level. True Lineage book?
By RAW, no. Page 86 of the corebook says "for every possible Hermetic spell, there is a corresponding Ability". Level 5 and level 10 DEO are different spells, so they get different spell mastery abilities.
Another good reason to get Flawless Magic.
That is exactly what OP is looking for: specific to General spells and allowing access to every mastery discovered with any variants.
The only difficulty is that spell mastery is typically locked behind a neomercurian or cult of mercury affiliation, but yes, it's awesome for a lot of reason - the main one being not having to restart your spell mastery progression when you want to upgrade your spell.
For a more complete answer:
If you look in the core book and at GotF, by RAW it is quite clear that one Mastery Ability applies to all levels of such a spell since the logic says so and the examples do exactly that. But then they wrote Adaptive Casting. But if you look carefully at what is in HoH:TL, you'll see that Adaptive Casting is contradictory; if its rules apply, it must not exist. So David Chart changed things around. As a result, don't refer to Adaptive Casting in HoH:TL. Go to the errata instead. David has ruled that different levels of spells like DEO are not different levels of the same spell, but are just similar spells, and so they do not share the same Spell Mastery Ability. To go along with that errata were issued for books on Spell Mastery that didn't have specific levels to give them specific levels. And Adaptive Casting now lets your Mastery Ability apply to similar spells.
So, to summarize, do not look at Adaptive Casting in HoH:TL like others are saying. This only leads to the aforementioned problems. Take a look at these in the errata.