That hits on another obscure (quasi-)rule that I'm not sure everyone always adhered to: that dungeons were supposed to have clearly distinct and increasing difficulty levels within them corresponding to how many floors underground you were.
Sticking to this idea rather narrows one's options when designing adventures.
It was always described as a guideline for the standard dungeon style play, intended to help players make smart decisions and play the "press your luck" game. But the encounter tables also easily allow you to encounter more deadly monsters from the more dangerous levels of the dungeon, even if you're sticking to the easier levels, so it's clearly not intended as a concrete rule that you can't encounter a higher level monster on a lower level dungeon level.
And it's pretty clear that it was never intended as a constraint to creative adventures designed to be played differently than the standard multi-level dungeon crawl. Steading of the Hill Giant Chief was the first module TSR published, after all! The first two modules ever published were Jaquays' F'Chelrak's Tomb and Wee Warriors' Palace of the Vampire Queen. As far as I can tell PotVQ does function with higher dungeon levels getting more difficult (though you start at the ground level and work your way up), but F'Chelrak's tomb doesn't function that way.
So in practice we don't see that it narrowed the options for adventure design, when you look at published examples from the period, at least.
Natch, not quite at your hand but as Lanefan noted you still need to line yourself up, which while perhaps not as automatically dangerous as needing to be adjacent to the start point it was still more difficult to achieve and potentially isolating (and still all reasons why the reflectivity made lightning bolt more worthwhile as an option vs fireball back then than it is right now I'd say).
"not quite at your hand" seems like a serious understatement when we're talking about being able to start it at least 90' distant from yourself in all cases, and farther as you gain in levels!
I'm pretty sure that's an incorrect version of how the spell is supposed to work. If you get "hit" twice by the bolt, you don't take double damage. Instead, you need to succeed on two saves to take half damage (basically, disadvantage).
1E is not clear about that. A lot of folks (Lanefan has attested his group being among them) interpreted it as being hit twice (ie: double damage), and treated that as an advantage of the spell over Fireball, which is the same level but covers a much larger area. 2E did change the spell description to explicitly work the way you're describing, but then, 2E also caps both spells at 10d6, so 2E in general was down-powering some spells.
I'm curious if anyone knows the rationale here- as I understand it, a normal human starts being slowed down when they carry more than 20% of their own bodyweight, and here I have a character who can carry around over 150% of their own bodyweight and not care, and then suddenly another 40 pounds and they're staggering around at half sleep, lol.
Every Encumbrance rule in every edition has the same issue of having arbitrary break points where you pick up one more dagger or coin and now you're suddenly slowed. This is just the nature of the beast.
The break points on the categories are, AFAIK just arbitrarily chosen to match standardized movement rates. I supposed one could do a calculation with a calculator or slide rule (or longhand on paper!) to proportionally reduce movement speed based on what percentage of your maximum weight carried you're currently toting, but that seems a bit annoying and impractical. Every time you pick up or put something down doing the calculation again? "Ok, I with the loot from the last room my movement rate is now 25.6'/rd!"
Another obscure rule: as far as I'm aware, there's no explicit statement in AD&D 1E that the monsters can deviate from their alignments as listed in the Monster Manual.
While the AD&D 2E DMG seems to (if I recall correctly) explicitly echo this sentiment, PHBR10 The Complete Book of Humanoids walks it back, stating that individual creatures can have any alignment.
EDIT: I'm pretty sure the 2E Monstrous Manual also, in its introductory section's notation of what a monster's "Alignment" entry meant, explicitly stated that individual creatures could have alignments different from what's listed.
As Snarf pointed out, the 1E MM says this is the monster's "characteristic bent". I read that as synonymous with "typical inclination". We're talking about abstractions covering broad groups. It seems obvious to me that there will always be exceptions to such descriptions unless they're explicitly ruled out.
