Its all complicated...
Giulietti designed accordions but got others to build them for them. For the past few decades Giuliettis were made by Zero Sette. Zero Sette itself became part of Bugari some time within the past two decades or so. The two share space at venues like the Frankfurter Musikmesse (but each have their own representation with Bugari much bigger than Zero Sette) and most of their instruments look virtually identical. They share the same factory which has the Bugari logo at the top left and the Zero Sette logo at the top right.
Petosa I dont know much about...
Have a little patience with me on an answer to your ??'s on your accordion.
You see us here in New England are living with the remnants of a snowstorm & power outage's .
I did know Julio Giulietti personally, his family & business as he was only 20 miles from my home.
Give me a day or two, and I'll respond to your post & ??'s.