Lanefan
Victoria Rules
All this shows is that rules trumping in-fiction logic isn't just a WotC-era problem.Snarf is on the money in every detail.
In OD&D and AD&D class restrictions on weapons and armor are absolute. AD&D non-proficiency penalties are for weapons allowed to your class which you don't happen to be proficient with. If a weapon or piece of armor isn't on your allowed list, you may not use it under any circumstance.
Per the rules for dual-classing (The Character With Two Classes, 1E PH p.33) if you dual-class and in an emergency use an weapon or armor or other class ability from your old class while adventuring as your new class, before you reach the point of having exceeded your old class level, you can do it, but you gain zero experience points from the adventure. Working from that precedent, it seems like if your suspension of disbelief can't countenance an absolute prohibition, the most natural house rule would be that if a regular MU or whoever uses forbidden gear = zero xp for the adventure.
There is an absolute ton of contemporaneous discussion about (e.g.) Magic Users being absolutely unable to use prohibited weapons under any circumstances. This was a frequent player complaint/subject of disbelief, and Gary confirmed it in editorials as well.
And that even 40 years ago I was already making the rules fit the fiction rather than the opposite.
