My January 2021 US Aircraft Registry shows 89 BD-4s with valid registrations. In addition, there are an additional 190 BD-4s listed as being de-registered. So in the US, at least, there have been almost 300.
Ah, but that's why a lot of folks don't like the Bede line. It's *not* one company over fifty years. It's a string of them, with a number of buyers left holding the bag (BD-5, B-10, BD-12/14). I haven't heard of similar shenanigans over the BD-4, but the Bede name got a well-deserved bad reputation from these other programs.
Friend of mine was kind of the main source of support (non-Bede) for the BD-4 line. He had one, and was very positive about it. However, there were some quirks of the design that builders needed to address.
Ron Wanttaja