Hi Ginger,
don´t worry about the missing word "Calendar" - this is quite common!
I rather would worry about the Cal. 502 movement - as this Ref. should have a Cal. 503 inside...
Have you ever tried to confirm (opened the back)? Can you post an image? Maybe a mistake of the seller?
If you look up Ref.2849 on the Omega official website you will find the info.
But the Omega website is not always perfect and complete - sometimes there are slight mistakes or something is missing (as I have experienced).
The best way to ease your mind was an extract from the archive though.
Or maybe Bill can chime in and tell us what he knows - maybe he knows more about...
I hope I could help a litte...
kind regards
Erich