It's a run of the mill POST-BAN Maddi. ARM was just one of the later names they were brought in under. Obviously the post-ban date (3/2/96) on the certificate was a giveaway. Marks on the gun, like the date or "ARM" are more important than the cert. so check for those as well.
The one-piece stock is almost certainly a thumbhole with the bridge cut out. The thumbhole profile of the Maddi was very different to the thumbholes on other AKs like the MAK-90. It had a very thin piece of wood between the butt and the pistol grip shaped portion. Easy to get rid of and looks natural when cleaned up and refinished. The refinish job is probably the reason the furniture looks so good in the first place.
The good news is they are great AKMs and were built on Soviet machines set-up by the Soviets for the Egyptians. About as close as possible to a real Soviet AKM as you can get.
The bad news is unless there are a few US parts on that gun, it may be in an illegal configuration (I'd say 99.9% chance of that) because of the now pistol grip. Check for US parts, but I wouldn't sweat it too much. You can easily fix it if it doesn't have US parts in it.
Ross