The strengths for above 18/00 are either in the DMG or the Monster Manual, they aren't meant for players

Anyways, I know I've seen them in the 1E material. If nothing else, they are with the Giant Strength Belts.
But yes, the chart never went to 30, I imagine that's a hold over from the original D&D (which I never played, so I don't know for sure)
It could be that at some point, 18 percentile wasn't being considered and the different break points in the percentile were separate numbers, ie, 18/(01-50) = 19, etc. Then the chart would be extended accordingly. But they probably changed it to percentile to indicate it was still in human range.
Mechanically, 1E and 2E aren't all THAT different, other than the profiencies (which IMO, aren't done all that well) Class wise, I think 1E was much better, a 1E druid was SO much more fun than a 2E druid, it wasn't just some type of cleric. It's also fun not to have upper limits on spells like Fireball, a 20th level caster would get that 20 die fireball, which was fun to roll
Mira (Life's a beach, and then you drown.)