Datejust with 16233 and 16200 markings?

[rolextician]

I may have an opportunity to acquire an one-owner Datejust from 1990 (E-serial series) but interestingly, the caseback serial is 16200 but the serial number engraved on the watch between the lugs says 16233. If I've understood correctly, it seems a 16200 is a pure Steel model whilst the 16233 is a two-tone model.

Does that mean the caseback was replaced at some point? I'm attaching photos to see if it helps?

Add* Also, it doesn't have a cyclops lens. Is that a normal thing? I thought all Datejusts were fitted with them.