Mike, a simple question, but complicated to answer! First, nearly all the Mauser, Oberndorf commercial actions have the “thumbhole”, patented by Mauser as a means of gas control if a case ruptured. Only few actions with solid left walls were made on special demand from the mid-1930s on.
Before WW1 the Mauser patents were still valid. DWM, mother company of Mauser, made military rifles for the international trade only and left the civilian market to their subsidiary Mauser. The government arsenals Spandau, Erfurt, Danzig and Amberg, were allowed to make military rifles for the German armies only. Anyone wanting to make a sporting rifle with a M98 Mauser actions had three ways to go: Reputable gunmakers had to buy an a commercial action from the Mauser, Oberndorf factory first. At those times the Mauser factory sold more than 70% of their commercial production as “actions only” or barreled actions to other gunmakers.Or he could buy a complete DWM military rifle from a production overrun through the international arms trade and tear it down for the action. And then there was a grey to black market. “Junk” parts that did not pass the stringent military inspection were scrounged from the factories, both DWM and government arsenals, reworked and completed into usable actions and sold to gunmakers. Many such actions went to England and were used by Rigby’s competitors.
This all changed after 1918. Hundreds of thousands of ex. Gewehr 98s and Karabiner 98s had to be demilitarized. At those innocent times cutting off the foreend and removing the bayonet lug did the job. The actions were scrubbed off the military markings and were used to build sporting rifles. In Suhl there was another source for unmarked actions: From 1915 to mid.1917 the making of Gew 98 rifles was decentralized to meet the war demand. All the Suhl and Zella-Mehlis guntrade made parts to be assembled and marked to complete rifles by Sauer&Sohn, Simson abd C.G.Haenel. But none of the Suhl factories were equipped to machine receivers or some other complicated part. So the Suhl guntrade was supplied with machined receivers by the state arsenals and less likely capable companies like Siemens&Halske and H.Pieper in occupied Liege. As the demand of the shrinking German armies was met in mid 1917, Gew 98 making was stopped quite suddenly. So tons of unfinished and unmarked parts were left over. These served the Suhl guntrade through all the interwar years. Suhl dealers exported such new actions made from these stocks too. So there are two possibilities for your unmarked actions: They may be scrubbed ex-military or they may be completed and assembled post-WW1 from left over and new made parts.
Axel