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What is your source for the V and VI gruppi?
From Pignato e Cappellano's Gli autoveicoli da combattimento dell'esercito italiano vol secondo.
PP. 1287-129 lists the III, IV, e V gruppi corazzati Nizza with autoblindo. While some operational history is provided for the III and IV, none is given for the V gruppo.
I have found nothing in this book that states that the IV gruppo corazzata Nizza was a mix of autoblindo and L6/40s. PP. 199-202 discussing the employment of the L6 and doesn't list the IV gruppo cor. Nizza as a unit with this light tank.
From L'esercito e i suoi corpo vol. secondo, tomo II
P. 453 (schema 9) and p. 457 also list the III, IV and V gruppi cor. Nizza. What is different is the III gruppo is listed as L6/40. This doesn't match Pignato e Cappellano and I believe this is incorrect. Operational history is provided for the III and IV gruppi (pp. 457 e 460), but nothing for the V gruppo.
From Benvenuti's I carri armata del Regio Esercito vol primo (this is the collection of armored volumes from the Fronte Terra series).
The published volumes don't include the A.B. 40/41 series, so I can't check for the number of gruppi from the Nizza. It does have the volume on the L6. PP. 64-82 discuss the operational use of the L6. Here on p. 79 it does state that the IV gruppo was a mix of L6/40 and A.B.41.
Ceva and Curami's La meccanizzazione dell'esercito fino al 1943 actually touches on this issue. Tomo I appendice III (p. 487) lists three gruppi Nizza autoblindo (III, IV, and V). No mention of L6/40s in IV gruppo, just a statement that all three gruppi had 40 autoblindo. Footnote 3 (p. 491) discusses whether the V gruppo existed. They cite the same pages in L'esercito e i suoi corpo that I referenced and agree that the III gruppo wasn't equipped with L 6/40s. In conclusion they believe the V gruppo existed, originally planned for A.S. but ordered to Sicily in 1943. They reference a discussion with Ambassador Umberto Bozzini, a cavalry lieutenant s.p.e. at the time and apparently knowledgeable about these units. No further details are provided.
So three sources state that the V gruppo existed, but none give any operational history. No source states the VI gruppo existed.