Yes, Helen, perhaps I did see Serov's portrait (ca.1900) at Tretyakov, not at the Russian Museum. But I was surprised at how small it was, and the general appearance seemed unfinished -- preparing for the final oil version, I suppose.
Interesting, too that Lipgard's is at the Alexander Palace. Someone must be keeping track of where all these portraits have ended up after the scattering in 1917. If not, it would be a worthy task!
I am fascinated with how modern people, especially Russians, react to Nicholas (in his many interpretations). His portraits are an eye into how people viewed him during his lifetime. Some are propaganda (Lentulov's, though I love it), some look as if the artist didn't like him (Repin's several, in my opinion) and others like Serov's look into his private world -- which makes it a special painting.