Hi Dale,
I think that the gentleman collector that you refer to as being named adjacent to the back b/w view of the tiger is Donald Stoehr. There are a number of obituary notices for him, if the same person, but I have not seen anything that references a specific interest in Nihonto or fittings.
To the best of my knowledge, the tiger pair were split ( under contentious circumstances ) in the early 2000s.
It is quite likely that the original and still missing piece ended up with an east European or Russian collector after the Nagel auction. This was getting on for 20 years ago and so it could have changed hands multiple times since then.
Images of the Utsushi that Ford made have been freely available on the internet for many years also. Sites like pinterest have shown it for a long time, so it is no wonder the Chinese fakers have picked up on it.
Obviously, it was only after the views of the back of the tiger tsuba became known to us that it was possible to compare Ford's Utsushi with the original. The more complicated treatment of the point where the tiger sits was an interpretation of the available information from the front view ie. in that area, almost nothing. I remember having long telephone and Skype conversations with Ford about that area on the piece , and eventually deciding to go with the paws and exposed bamboo framing, all of which were very difficult to blend convincingly.
As I am sure you are well aware, there is more background information and commentary to see on the 'A series of fittings' thread - for those who are unaware or would like to revisit, the relevant Item Nos. are 306 and 307.
Best
Bob