1960s Murano Somerso Bowl

This is a Somerso bowl, I believe from Murano. It was purchased in Italy in the early 1960s by a family friend, who brought back with him as a gift for my parents. Height is 4 inches, width is 3.75 inches. If it had a paper tag or label, I'm sure my parents removed it at the time. So, I think I know what this is, where it's from, and roughly when it was made, but I've always wondered about why two of the bottom base corners are squared off, while the other two are rounded. Is this an indication that it might have been a second, perhaps with two chipped corners that needed to be cleaned up? Or is this base treatment associated with a particular factory on Murano? If you know and have time to leave a comment, thanks in advance!