There is some pretty well placed, though still anecdotal to this point, evidence that the 9,0-9,5mm booster nozzles are original wartime German issue, but for a very refined purpose.
Despite the huge metallurgical and machining technology advances that the Nazi's enjoyed in making their weaponry, they were still confronted with the same serious issues that everyone else was when it came to having access to suitable high quality weapons lubricants. For the most part, they spent the war like almost everyone else, with a less than ideal lubricant situation in that they always used petroleum-based, or later synthetic esters (coal oil using Bergius hydrogenation process/Fischer-Tropsh process/or PAG-polyalphaolefins) which all still performed like petro's in the environmental aspects. In very, very cold weather.....like that found auf die Ostfront, all petro's became unsuitable due to thermal viscometric properties that basically turned the lubricants into glue. The only solution was to continually heat the metal surfaces....any way possible......or, simply run the guns absolutely bone dry, sans any lubricant. German war time lubricants were generally used uninhibited, and no inhibitors or additives were used in almost all cases, the one major exception to this was in weapons lubricants where two purpose-designed additives were employed regularly. The first was the common "flowers of sulfur" which was nothing more than finely powdered sulfur that when added to the oil bonded to the metal as a metal sulfide coating adding a measure of anti-scuffing protection. This was abandoned with time as a more modern and refined version known as "Mesulphol" which was a synthesized product that was (usually) combined with a competing-action anti-corrosive substance additive known as KSE (korrosionschutzester). Despite the radically improved lubricant properties, these lubes were still at the mercy of extreme low temperatures and their attendant problems.
One of the measures taken to alleviate sluggish running was to increase the available system energies in the recoiling parts and this was ostensibly documented to be the source of the smaller diameter booster nozzles. Currently, the only sources for this information seem to limit the discovery of these parts only in guns issued, or found later, in areas where fighting took place in extreme cold conditions. Guns known in Finland, the Baltic States and Ukraine have been shown equipped with the smaller booster nozzles, as discovered. The theory seems to be consistent with the notion that the smaller nozzles were intended to impart a starting energy that was significantly higher as to overcome any tendency for the lubricated surfaces to resist movement, or alternately, for any un-lubricated surfaces to adhere from frosting. Once running, available heat from combustion and friction was probably generated to warm the larger surfaces sufficiently to keep the gun functional for a reasonable duration.
Other combatants generally, particularly the Finns, ran their weapons completely dry in arctic conditions preferring the accepted levels of wear over tendencies to fail to fire. The Soviets went in the other direction and completely went away from petroleum based lubricants and even HC synthetics, and developed a wide range of excellent animal fat based synthetic lubes, to the extent that almost all Soviet vehicles never saw a drop of petroleum oil or grease, ever. The Soviets issued no weapon-specific lubricants; one used what was available so probably everything imaginable was used, some with good results, some bad.
It seems now entirely probable then that these 9,0-9,5mm booster nozzles were completely normal issue in certain areas for assisting with functioning when faced with a still vexing issue of less than perfect weapons lubricants. There does not seem either, to be any records extant that document this as logistical fact, only the guns themselves so equipped survive to tell their story. And since so many of the "parts kits" guns came from these areas, it should some as no surprise really to find these smaller booster nozzles in many of this origin of kit gun.