The 21st Italian Army Corps had the following staff in October 1940:
----21.o Raggruppamento d'Artiglieria di Corpo d'Armata con:
----I/21 Gruppo da 105/28 (pezzi da 105/28)
----II/21 Gruppo da 105/28 (pezzi da 105/28)
----III/21 Gruppo da 75/27-906 (pezzi da 75/27-906)
----IV/21 Gruppo da 75/27-906 (pezzi da 75/27-906)
----13/21 Batteria da 20/65 antiaerea (pezzi da 20/65)
----14/21 Batteria da 20/65 antiaerea (pezzi da 20/65)
----21.o gruppo contraereo da 75/27 CK
----21.o Reparto Specialisti di CA
As for the defective artillery charges, it was actually a frequent occurrence, so much so that even in the official stories of the British, Indian, South African and New Zealand campaigns, the thing is often remarked and underlined. However, it would be actually interesting to know in which official Italian report it is reported because I have never seen it reported in many years of research in contemporary Italian sources.
All the best
maurizio