Honestly, if this were mine, I would be very hesitant to call it a Boucher. I have dug around online and seen this brooch in a few different platforms, being sold as Boucher and referencing a different brooch when trying to attribute it to him. The design on the two different brooches is different, and I personally wouldn't use that as evidence that this is Boucher.
I have only come across one piece of unsigned Boucher, and I didn't even realize it was his until after it sold (for way more than I thought it should have!) That was a much older sterling piece, that still had the stock number on it, and I was thinking the Phrygian cap mark had worn off over the years.
The construction of this piece does look very high quality, and it is a very pretty brooch, but I would definitely not feel comfortable calling it a Boucher in a listing title. I may mention in the description that it is very similar to a Boucher piece and give reference to the 1042P brooch that has similarities, but I wouldn't go further than that.
You could also post this to the other jewelry forum, Jewelry & Gemstones Board Group, as they get more traffic and someone there might be able to help identify this for you.
