I have seen this formula expressed as "less than 30%" and as "less than 20%." Which is correct? Was it changed (fairly recently)?
Both are correct! The rules are different for each of the three NCAA divisions, different again for NAIA, and even more different if the player was injured at a 2 year college. Any player who was injured before transferring may take the more favorable ruleset. In all cases the rule is more complicated than just a percentage. So if you really need to know the details of the hardship waiver, see 14.2.5 in the D3 and D2 Manuals, or 12.2.4 in the D1 manual.
On the other hand, perhaps you're just curious. Very roughly speaking, D3 requires not more than one third, D2 not more than 20%, and D1 not more than 30%. For many situations, NAIA only requires that the injury be season ending, regardless of how many games have been played.
Thank you 3FG!! I was curious but also trying to nail down the answer as it relates to D1 and finding myself confused. Appreciate the clarity very much.