Bunny, I'm thinking this might be one of the early Lightweights. There's no pic of this bag but my Fall Preview 1989 book shows a zipped Light Tote #4065 with the same squared O-rings on the strap handles and mentions using an industrial zipper. It also has the same kind of strap "extensions" going from the handles to the base of the bag. There's also a Travel Tote 4085 with the same features. And maybe the Lightweights used a lighter metal on the zipper pulls and just brass-plated them?
YokelMel, the Lightweights (which later became the Sohos) were a line of bags in which Coach DID use lighter and thinner leather and also lighter-weight hardware to keep the weight of the bags lower. A lighter-than-usual bag often is from this line which I think came out somewhere around 1987-1989 which would also fit in with your bag's serial number.
Bunny, just guessing that maybe the problem with the zipper could be one reason it's stamped as Irregular? Or maybe the zipper or pull might have been broken and replaced at one time. The industrial zipper on the inside is exactly what Coach would have used though.
I only have one Lightweight and it's a zip closure, not magnetic, but give me a little while to dig through the closet and move a few things out of the way - there might be something on it that will help.
Thank you Hyacinth!