If it was difficult to tell whether bronzed or not, then it was probably a Taylor restrike which are passable to notoriously blotchy in their toning. You never see the even bronzing achieved at Soho, which is also darker than Taylor's.
There are a good number of ex Boulton pieces in the market now. Obviously MPWB had a good number made of quite a few types which were retained by him and passed to his descendants. They have been coming out in dribs and drabs for the past 15 years or more through a multitude of channels. The one you mentioned in Heritage will have come through the guy who runs the Copper Corner, as he acquired a good number of them. They were also sold through various dealers in this country. I bought some that were listed in the Circular in 2007, which were all ex-Boulton too though not listed as such.