"New ones only come with a Modified installed choke, older ones had three."
That has not been my experience.
My uncle won an Express the first year they came out in the late '80s and it only came with a MOD choke tube. It was a magnum even though it didn't say Express Magnum on it.
I bought an Express Magnum in 1993 and it only came with a MOD choke tube. I got it at a steal of a price for back then - $199.95.
Both of these guns came with gunk on them that was probably preservative and looked like funky rust when rubbed off. I've used mine exclusively for saltwater duck and goose hunting and haven't had any problems with rust since I started spraying religiously with BreakFree or Sheath after every cleaning. Not after every use, after every cleaning - like on Monday night after a weekend of bouncing around in the skiff and dragging it in and out of blinds and swamps and stuff.