There's another page on the subject with some good information and suggestions, and a source stating that the abbreviation was not in widespread official use in that time. 


https://latin.stackexchange.com/questions/1872/is-qsd-an-abbreviation-for-a-latin-phrase/2042#2042?newreg=0327f55252a34fabbc849b95383f9d08

Perhaps the writer was fond of the word "Questioned"... This is to be questioned, my brother. You have much less chance of finding good interpretations if you only post one example in context, as the context is of major importance in all it's instances.

Quis Sicut Deus.
"As I said before," quae supra dixi.