60s Constellation 'Solid Gold Dials'

Hi Folks need some information and help. Looking at solid 18k Constellations and adverts seem confusing when it comes to dials.
Looking for caliber 712 with solid gold dial. Some claim the dial is solid gold and the dial shows 'om' printed either side of the 'swiss made' just below the 6. I have been told this is abbreviation of 'Or Massif' which does translate to Solid Gold. I have noticed that not all dials that sellers claim are Gold have this marking on the dial. Were some manufactured without 'om' but can still be gold? or are only dials marked 'om' solid gold dials.

18K Constellation with gold dial (ref. 2799 from 1954)

Not all have the OM!

Thanks for that but just realised the watch I looked at was '67' without the 'om' mark so that should be marked?

Yes Im a complete idiot and got it totally wrong, your very kind to even bother to answer. Coupled with it is my first time on this site all helped confuse an old fart which is probably my main problem. The watch wasn't a Cal.711 for a start it has a Cal.751 its is stated as 1967 ref 168.029