Old building with MC cable running on roof feeding lights. Probably 20+ years old. Thank you for your help.
Short answer you will need to figure out the year it was built/permitted and figure out the exact cable type. ACL and ALS were allowed outdoors.
Longer answer:
The 1928 NEC 505j mentions a type of AC called ACL cable that has a lead sheath under the armor that can be used outdoors or underground. The cable was last listed in the 1990 edition. The lead sheath under the armor makes the cable really heavy, is very noticeable when doing demo and of course workers should use caution demoing it (Cutting it with a sawsall should be avoided).
In the 1959 NEC type AC was first required to have that bonding strip in it, so you can date a system by looking for that strip.
In the 1962 NEC a new Article was added for Aluminum-Sheathed Cable type ALS cable (MC also first appeared in the code in 1962 when Article 334 got renamed after it).
ALS cable seems like the aluminum MC we often see today as 'MC-Lite' the 1962 331-2 allowed ALS in dry or wet locations ( but no corrosive)
Perhaps someone whom worked with ALS cable in the early 70's can chime in?
ALS continued up to the 1975 NEC when the article got deleted.
The 1978 NEC split MC and AC into different articles.
Cheers