I think that using the magazine count for identification purposes is extremely limited. For one thing, there is always the question of including a ball in the barrel or not, so, any count can go up or down depending on how you want to count it.
Also, I think that Beeman misread Haller, because the reference to 20 shots in Haller has nothing to do with magazine capacity it's about how many shots the gun had to achieve with a single air tank. Each gun had to be tested to prove that it achieved the required 20 shots, before being accepted. For whatever reason, this has been interpreted as the magazine capacity.
Regarding Beroaldo Bianchinis, I'm not sure that he had an original Girandoni to work with; the 24 ball magazine count being one of the reasons to suspect this. It appears that "Girandoni" became a generic term for any magazine fed airgun of the Girardoni type.
Can't recall if I brought it up on this forum, but what appears to be a true Girardoni-made example appears to have been located in Germany. The reason we can be pretty sure that this gun is a true Girardoni is because it is inscribed "Girardoni - inuenit et fecit" Inuenit et Fecit is latin for "I invented it, I made it."
And, as expected from the original documentation, this gun, according to the museum, is a 14mm gun (probably 13mm in reality, with the 14mm measurement being made at the muzzle) Magazine count, according to museum, is 22.
The gun described in Baker/Currie is almost without question based on the design of Nemetz; for an improved Girandoni. This is based on the information provided in the article by Hummelberger. Hummelberger clearly made an error in judgement when he wrote that this clearly noted later design was something other than the Nemetz design (proof of this is contained in part 2 of Hummelberger).
Sorry if it seems that I am "gloating" about finding more information on the Girandoni; from my perspective, it is more a case of marveling about all the information that is available to a researcher willing to dig into the subject. I was amazed at how little had really been done. Note that this is the exact same thing written by Arni Hoff in the preface to his wonderful book.