This illustration from 1820 was in Skail House near Skara Brae and though it’s titled ‘Stones of Stennis, Orkney’, it’s clearly Brodgar. Possibly there was no distinction between the two sites or maybe the title is just very literal.
Image credit: A R Cane
I'm sure you're right though isn't it the case that there certainly were more stones at Stenness than the few left standing today with some serious vandalism having occurred in the 19th century?
Yes, I think I read somewhere that there were originally 16 standing stones at Stenness (bit of a mouthful!), followed by the usual vandalism of later centuries, but there appear to be 19 in this illustration.
Historic Scotland website says Stenness was originally a circle of 12 stones, but the 1820 illustration is clearly the Ring of Brodgar with Salt Knowe closeby.