How's this for brain-picking, Blake?
9x17mm - 9mm Browning short/Kurz/short/Courto/380 acp etc.
9x18 Ultra (WW2 and re-introduced in later years)
9x18 Makarov (larger - 9.2mm Russian developed)
9x19 Glisenti - dimensionally same as 9mm Luger loaded much lighter truncated bullets to differentiate from hotter 9mmluger/SMG loads.
9x19 - Luger/parabellum/nato/Patronen 08 etc.
9x21 Several similar rounds. Introduced in Italy where "military calibers" not allowed to private owners, another used in competitive shooting in USA to make major caliber.
9mm Browning Long (9x20~) Swedish, Spanish, and others
9mm Mauser (9x25) not experimental but saw wide use in Broomhandles and SMG's.
9x23mm - Bergman bayard, Campo Giro(?), Steyr
9mm Mars - experimental semi-production for the British Mars Series of Pistols. bottle necked load.
Confused enough? Good! So be careful and read the labels!