There were only two brothers, Ugo and Cesare. They split up in 1982 and Ugo kept the Rossi brand, Cesare split off and continued under the NovaRossi brandname. At some point in time Ugo's son Alessandro (I believe) took over his fathers company and changed the name to AXE Rossi. But other than regular development, he did not change anything basic to the engines AFAIK. Therefore to my knowledge the AXE Rossi's were just regular Rossi's but the Alessandro fancied colourful anodizing a bit more than the boring black.

But I have never understood much of their type designations. So I cannot really help out there either.
I would just run it. All Rossi engines are brilliant runners IMHO.