It's about 1992 - 1994 (I can't remember when they riveted them on from the bolts.
Probably just 1992, there should be a 'two letter' datestamp on it somewhere, e.g. PK on many 1992 'model year'
Should see it on the cogs iirc.
You can just see one of the flaws as it looks like the screw is coming loose.
Quite typical, though the top one bolts often disappeared somewhere during a ride
Looks to have spent most the time on the road as it's the lower cogs and one middle that is most warn. Should be ok, certainly better than many you see and great for someone like me who picks up spares/repairs to pull the odd cog off it. (I wouldn't as you could probably sell it for much more than I would pay).
Split from the wheels if M900/M737
If a lower model, then leave them on.. I would have though.