Regarding the decal sheet, I have been going over my numerous sources to compare to what you have, and see if my prior knowledge and understanding is open to interpretation. I have come to the conclusion that your sheet has errors.
Regarding the red, blue and yellow rectangles (used to denote company), you are CORRECT regarding the white vertical bars to denote platoon (1st, 2nd and 3rd). And you are CORRECT to provide some colored rectangles with no white vertical bars (these were used for the Company HQ vehicles).
However, you are INCORRECT when you show the vehicle number in white over the colored rectangle. The vehicle numbers were done in the same color as the rectangle. So red numbers for 1st Company, blue numbers for 2nd Company, and yellow numbers for 3rd Company.
Regarding the Semovente decals, the use of triangles was an Ariete Division thing (for sure), and possibly a Centauro Division thing (still researching). But the Littorio Division used colored geometric symbols. I have it noted they used red circle, triangle, diamond and square shapes.
I have not confirmed if it is always red, or only red for the first company, and perhaps blue for the second company and yellow for the third company. I have not confirmed if all vehicles in a company use the same shape, or if it is (perhaps) a circle in HQ platoon, and a triangle (for 1st platoon), and a diamond (for 2nd platoon) and a square (for third platoon). (still researching).
And in case anybody cares about those Semovente decals, the triangles point downward for Company/Platoon vehicles, and they point upward for HQ vehicles. Also, Semovente were organized by "battery" and not platoon, and the colors are as follows:
1st Battalion, 1st Battery (white). 1st Battalion, 2nd Battery (black and white tip)
2nd Battalion, 1st Battery (yellow). 2nd Battalion, 2nd Battery (black and yellow tip)
All four of these are provided for on the decal sheet!
I have seen photos of Semovente with the black and yellow triangles, where the triangle has a black outline. These decals are also on the sheet. I have been unable to discover why some vehicles had the black outline, and others do not.
I commend you for adding them (since there is photographic proof those are legit sometimes), but might I suggest dropping them for something else?
Along the right edge are some MISC decals, and those trios of decal types are all terrific. But there is one missing. You have three black rectangles. Great. Those would be used as the basis for Battalion HQ vehicles. But missing would be three white rectangles, which would be used for Regimental HQ vehicles.
I don't know if people are going to be interested in representing regimental command vehicles, so perhaps having the white rectangles is not necessary. But you are including battalion (black) rectangles, so thought I would point this out.
Loving the 21 license plats offered up!
Finally, I am still researching the Roman Numeral Battalion IDs provided. You have 11 battalions listed. The Italians had a grand total of 32 armored battalions during the war. Some were of course, assigned to the armored divisions. Many were independent units, or units assigned to motorized infantry. I have not concluded (yet) which battalion IDs are more useful, given that there is no way to include them all on a single decal sheet.
Hope this info helps.