Hi Paul,
I am new to Gmic, and since I am a longtime collector of worldwide ODM I find this site quite interesting. As I have lived in Japan for some time, I have been able to collect Japanese ODM including the certificates. Your Masterclass on Japanese certificates is very useful, especially since the average collector would not be able to read them. If I may add some information which you will know already, but may be interesting to other readers. When the document would be signed by the Emperor the first column on the righthand side of the seal will read something like " under Our sign manual and affixed with the Imperial seal " wheras a certificate without the signature would only mention the Imperial seal. Interesting is that during the last year of his reign Emperor Meiji was sometimes too ill to take care of affairs of state. Certificates that would usually carry his signature were issued with only the Imperial seal, but the text on the certificate would still say under Our sign manual etc. I presume these certificates are scarce.
As you mentioned already elsewhere in this thread, when the Taisho Emperor became longterm ill, Crown Prince Hirohito became regent, and he signed with both his father's and his own name. If I remember correctly you wrote that you have such a certificate for the Rising Sun with Paulonia Flowers, awarded to a Brish Field Marshall. I don't have the figures including foreigners, but the number of Rising Sun with Paulownia Flowers awarded to Japanese during the regency is 20, and these certificates are therefore quite rare.