Am not trying to give a smart aleck answer, just an honest one. Your possession of 23 boxes of a specific type of cartridge would, in my opinion, rule out the use of the word “rare” of itself.
That’s a lot of ammo if one is considering the single-specimen collector, and probably enough for half the collectors of full boxes in that caliber in America.
However, regardless of that, these boxes, if they are of the “green label” type, are relatively common in the USA, as a great deal of this ammunition came to America about twenty years ago or so, probably along with the Chilean-Crested Steyr-Hahn Model 1912 pistols. A couple fo other styles of box that were reare in the US before that also came in from that country, including 50-round German and 16-round Chilean boxes from FAMAE.
The Geco box I am talking is labeled as follows (I have not attempted to duplicate the spacing of the letters, or their font):
Patronen für Selbstlade-Pistolen
"Steyr" 9 m/m
auf Ladestreifen Ganzmantel-Geschoss
Gustav Genschow & Co., Actiengesellschaft
The end labels say:
There is a back label as welljust basically telling about the ammo being non-corrosive and patented in all countries (in German, of course).
I cannot help you on values, but although fairly common, I am sure the boxes still have value
probably slightly higher than just surplus shooting ammo, especially the ones in best condition, and if they have the clips still on the ammo (If the boxes I am thinking of).