Rolling under the stat expresses Baker's three insights

[piou]

If it was widespread practice as a generalized method, then you'd be able to find some contemporaneous evidence of it.

Speaking about dragon there's a very weird method based on ability score in the very first issue that shows it was at least a question that was on people's mind, but it wasn't roll under your stat. Issue #68 (1983) however has an article titled "You've always got a chance" by Katharine Kerr that describes rolling d100 under your stat times 5.
More to the point there's also mention of what's essentially a d20 DEX save page 35 of Dragon #39 (July 1980) in the article Good Hits and Bad Misses in a fumble table:

01-19 slip; roll dexterity or less on d20 or fall and stunned for 1-4 rounds
20-33 stumble; roll dexterity or less on d20 or fall and stunned for 1-6 rounds
Etc in the table.

Similarly in issue #46 (February 1981) page 35: The weapons may be wrenched free in 2-8 melee rounds by a character who rolls his strength or less on d20.

And in #50 (June 1981) page 30 and later: To avoid looking into a monster’s eyes, a character must make a number less than or equal to his Dexterity on a roll of d20 every melee round.

Finally (because searching this takes time, not because there isn't more to find) in Dragon #61 (May 1982) there is in an AD&D adventure page 37: If the flesh is damaged by a blow or a weapon strike, the object creature or character’s form will explode, causing 2-16 points of damage to anyone within 1”, and 1-8 points of damage to anyone from 1-2” away who fails a saving throw against dexterity (must roll dexterity or less on d20).

Widespread? Probably not based on these examples alone, but the idea was certainly around and getting traction by 1982.

 

[Parmandur]

I have no direct experience, but I quite like the convrptual elegance of roll under stat. Maybe it wasn't common, but it outta have been.

 

[Knorrrssk]

Of course, something that is often missed is that multiplying your attributes by 5 and then throwing a d% is exactly the same as just rolling a d20 equal to/under your attribute. The one thing I like about the multiplying attribute by x and testing with d% method is that rather than applying a difficulty modifier to the attribute, you can change the multiplier instead. So a moderate task can be x 5, a difficult one x3 etc.