TNTwatch
路No.
Back then every distributor used their own reference number system that did not necessarily match up with what is used today on the Omega Vintage Database. I have no clue why they did that.
http://www.old-omegas.com/catde59.html
I believe the above catalog page is Swiss German and it doesn't use the same reference numbers for the Railmaster and Ranchero that are engraved on case backs.
If a watchmaker needed case parts back then, they ordered from their local distributor using local reference numbers. If a part was in stock, great. If not, then the distributor contacted Omega who was able to "translate" the request based on country of origin.
Someone gave me this Swedish catalog for ordering Omega crystals some years ago.
http://s7.photobucket.com/user/gatorcpa/library/Watch Photos/Omega Crystals List - Swedish
While the case references (and matching calibers 馃榾) are the standard ones we see engraved inside Omega watches, the crystals are ordered by a separate numbering system unique to Sweden.
My guess is that as Omega began taking over these local distribution networks in the 1970's, they went to a more centralized and uniform method of model identification for ordering spare parts.
Take care,
gatorcpa
The reference numbers in those brochures are sale/marketing reference numbers, and yes they need to be translated to the reference numbers that were engraved on the caseback. Most of the time though, this translation is not likely needed because to repair or service the watch, the caseback must be readily available while the sales/warranty papers may not.
Interestingly for @mac_omega, that Swedish catalog was for or from 1980/1981 and it already says "reference numbers" for those 4 digits "case numbers".
Edit: changed the years from 60/61 to 80/81.
Edited: