Sven - Keep going, this is mighty impressive and diligent research.
I suspect by the time you are done you will have a list including many more visits that previously expected, possibly including multiple return visits too.
This is what George Payne found when researching Ross's fellow Scottish contemporary (albeit separated by an ocean) James Braid.
I have managed to augment that in several instances, myths need busting sometimes, but it is only by increased access to disparate (digital) resources this is now possible.
Braid has over 530 direct design citations (so far) and they were most probably the two busiest architects ever, so to research the entirety is a life's work (if possible at all), so crowd-researching may be the only way to complete the task.
The rephrasing of history and debunking of myths is only possible with factual research, you are certainly doing Ross's deserved reputation a great service.
I am sure the DRS will update their view, as will Brad & others, with the new finds you are sharing so generously.
Cheers