His covers were advertised and sold weekly in Linn's until his 9/11 cachet cover. That cover was artistic/appalling and his ad never appeared again in Linn's. I have never been able to find a picture of that cover again.
He actually created at least seven** different 9/11 (Scott B2) FDC designs. I do not know the number produced for each design except for one which was a production run of 4. That is the "You Never Walk Alone" card. I own one of this one but my image will not display correctly and cuts the right side off a bit but it is below anyway. Of the five designs, this one has the most disturbing (to some), but entirely factual, images from September 11, 2001.
As to a date of death, the Jan/Feb 2020 First Days, lists him as "late" thus it appears 2019 is a better guess for his year of death, not 2020 as mentioned above. I too have found no obituary.
If you do a Google IMAGE search on "HIDEAKI NAKANO 9-11 fdc" all five will be pictured.
I lost someone in my life that day, Jeremy Glick, but it was in a field in Pennsylvania.
**He also used the Scott B-2 on another design but that was for The Star Spangled Banner, not 9-11.