As a follow-up to my last post on this topic I've asked Google about the Nabokovs, Google being a simple solution to most queries these days, and found in Wikipedia that

Ivan Aleksandrovich Nabokov (Russian: Иван Александрович Набоков) (11 March 1787 – 21 April 1852) was a Russian Adjutant general and general of infantry prominent during the Napoleonic wars. ..... Nabokov came from an old noble family based in the Novgorod governorate, where his father general Alexander Nabokov was a landowner. ....Ivan Nabokov died 21 April 1852 in Saint Petersburg and was buried in the Peter and Paul Fortress, near Peter and Paul Cathedral. His brother Nikolay was a progenitor of the novelist Vladimir Nabokov.

So it seems that the Nabokovs must have been aristocracy, although one would still like to have reference to some Almanac de Russie, or similar.

Charles