I didn't state the French stamped ALL Ruby pistols with French Stars in 1922, you did. I honestly don't know what the French did and when, I just know a few bits of references from books, and comments from fellow French collectors in France, along with my own observations.
Medlin states in his books, The French 1935 Pistols, and French Service Handguns, that the French had 588,000 Ruby type pistols in November, 1918. It was estimated that 968,000 Ruby and Star Model 1914s were purchased by the French altogether. What isn't exactly clear is if the 588,000 Ruby pistols, were just the ones in storage or if they included the pistols still issued to troops. In any case, a large number of pistols were put into storage after all small arms were declared obsolete by the French in 1919. Some of these pistols were shipped to the Finns in 1919. To my knowledge, none of the Finnish Ruby pistols have stars.
Based on what I have been told by a fellow French collector/researcher in NAPCA, and what some researchers shared with Medlin, is that these stars were applied to pistols as they passed through arsenal reworks in the 1920s. What I do know is this. There is a wide variance in the shape and size of the stars, so they were not standardized. That leads me to believe they were applied at different times and places. Nor is there a direct relation to stars and safety balls, some have one or the other, others have both or none. There are also plenty of pistols that have the stars that don't appear to be reworked, perhaps they were only checked for functionality and "accepted" and marked with a stamp. I also know in that numerous instances I hold credible, of the pistols that saw WW1 service and were withdrawn from French service before the end of WWI, these pistols have neither the ball or the stars.
I have seen a few French Army manuals all through the 1920s and 1930s and they continue to reference the Ruby, but make no mention of the star marks. One dated from 1920 does not show the safety ball, one from the 1930s does picture a safety ball. I don't think every pistol in French custody in the 1920s had the safety ball. Consider this. The French Unique Model 1917 was a post-war Ruby type pistol made in Hendaye, France. In 1940 the French started buying all they could. It is nearly identical to the ones made in WWI, but of a higher quality, and stronger, plastic grips. None of these pistols came off the production line with a safety ball, even the ones intentionally contracted by the government after the factory stopped all commercial production. After the Germans left, the factory sold many more thousand of their newer "War Model" with the internal hammer to the French government. These too were not sold with safety balls. One will find a few WWII produced pistols and War Models with the balls, but I'd say the numbers are no more than one in five. What does this mean? The French NEVER added balls to all of their Rubys, instead, it appears they were more of an arsenal rework, and that apparently differed between arsenals.
So this leads us back to your original question, and I say this, I don't think all Ruby pistols were marked with stars, just as you state not all had the balls marked. I would have to guess that the decision to add stars and balls was made on a local level. I have avoided all together the issue of when these pistols received the makers marks on the pistol and the magazine. That is a whole other can of worms.
One more thing, I'm not sure the safety ball was worth the effort. I myself, and another collector independently, have tested these Rubys in holsters and can't find any evidence that they help. Of more weight, when the Germans took over Model 17 production in Hendaye during WWII, they didn't waste their time with these safety balls. Instead, they got rid of that silly bulbous safety itself, and made the safety very sleek and modern looking. This was a much better solution.