Below is a photo of the SFM Soft Point cartridge and the Polish/German box they came in. I mentioned this box in my post above.
I know of the MAS 1925 No1 pistol in 7.65 Long illustrated in Zuck, but no nothing of any pistols tested in 9mmP in the 1920.
Your hint on the STA 1924 was very useful. Nelson in Vol II covers this gun which was in 9mmP. Development began in 1921 (so maybe there even earlier boxes) and a second version in 1922. The 1924 model was a pre-production prototype and about 100 guns were made. On 11 Aug 1925, production of 8250 guns was ordered, but only about one thousand were ever produced. Many of these were used in combat in Morocco. From the date of your box, this ammo was probably associated with the production order for the STA 1924.
The MAS 1924 was also covered by Nelson, but he lists it as chambered for the 7.65mm Long, and he makes no mention of a MAS 1925. A reference for the MAS 1925 would be appreciated.
After WWII French machine pistol development appears to go back to 1947 from my references. After WWII, the earliest French 9mmP ammo I know of is Steel case, dated 1945, with the “ATS 1945” headstamp. This company produced blue tip, red tip and unmarked tracer rounds in 1948 and the Woodin Laboratory apparently has a blue tip tracer from 1946 according to my notes. In 1949 they changed their headstamp style to the traditional 4 position layout with both brass and steel cases. SFM produced brass case ammunition headstamped “SFM 1948” and in the 4th quarter of 1948 began producing brass case ball ammo with the 4-position military headstamp. I think this is all the French production I have documented before 1950.