Busman, I didn't state your helmet is 100% postwar, but instead that not every M33 with anchor WITHOUT crown is a '43 - '45 rsi Navy helmet.
These helmets were in use (not only in storage) way after the end of the war, at least 'till late '90's and over, and, since the plain anchor was the symbol of the RSI Navy but also of the Republican, modern Navy, it's not easy to say for sure if the helmet is a pre '45 specimen or not.
About stencils, pre and post war, there are many, even more than one for the same arsenal. Yours is actually very similar to some (see the pic below) crowned, in use pre 8/9/43 (and after the armistice in south Italy, where the Italian Navy was still 'royal'), but frankly, by the pics above, I'm not able to discerne the hand made "correction" of the crown: and this job would involve not only the yellow but also the green paint.
Anyway, again, it's hard to state if that job would have been made in '43 or after the war, when tens of thousands of m33's, still bearing the crown, have been "de-monarchized" and reissued in service as Republican Navy helmets.
About the paint (and stencils): these two M33 came from the same arsenal (La Maddalena), but as you can see, the paint is very different (the first one matches in colour the one you have) and different are the anchors.
Consider that the second one is an almost mint specimen, not messed in any way, with all the war period features (rivets, liner, chinstrap and rectangular chinstrap rings)... I wish I could be sure that it is a genuine RSI specimen, but I'm not.