Originally Posted by bike_galpal

fwiw i think there is only one "weird catch" to this and i believe (thought i could be wrong) it's that MTB derailleurs are often longer than long cage road derailleurs, hence one of the pics here withe "Long (mid)"

might be wrong about those details but suffice to say there is more than just "long" and "short", i think there are in fact 3 sizes and which one is "long" often gets confusing.

it's purely semantic though, since if you're coming from a true short cage road derailleur, any of them will be longer.

upon further thought (if anyone cares about my thoughts.... lol) i think older MTB derailleurs are about the length of a newer road "long" so maybe they defined that standard, although they are now longer. older STX derailleurs and stuff tho are shortish maybe even shorter than the modern long cage road.