If there were any references using the longer name dating from the time it was actually in commerce, I'd be inclined to accept the possibility that some other references had been shortened. However, I can't find any evidence that the rose was ever called 'Herzogin Viktoria Adelheid von Coburg-Gotha' prior to 1999. The [von Coburg-Gotha] that the Rosenlexicon reference has does not look like it's meant to be taken as part of the rose name, but rather as a parenthetical aside to explain whom the rose was named for.

I do think HMF should respect primary sources. I'm inclined to think that if Welter had wanted to name his rose with the "von Coburg-Gotha" at the end, it would have been used at least once during his lifetime- certainly in Rosen-Zeitung, and other German-language publications. As you point out, Welter had already used the "von Coburg Gotha" in an earlier rose name, without any sources omitting it.

Even the references from the 1911 Garden series on rose parentage did not leave out parts of rose names, even if they did occasionally use abbreviations to save space (such as M. for Marie)... in this particular case they did anglicize the spelling- perhaps unintentionally- but I don't see any reason to assume they shortened the name given that none of the other early references were any longer.

I think the longer name is incorrect, and the result of a confusing entry in Rosenlexicon decades after the rose was introduced. I don't understand how nurserymen's typing skills could have obscured the 'real' name until after the rose was probably extinct.

Thanks,
Virginia