Every invention feature of the solution that you impute to
Nabokov--do alter egos really say they are so different in age
and appearance from their real selves, by the way?--makes the
puzzle less fair.

Is the following any help in answer to Jerry's question ? From Alice in Wonderland, Chapter II, The Pool of Tears:

 

"Who in the world am I ? Ah, that's the great puzzle! ..... I'm sure I'm not Ada (!) .... for her hair goes in such long ringlets, and mine doesn't go in ringlets at all; and I'm sure I can't be Mabel, for I know all sorts of things, and she, oh ! she knows such a very little ! .... I must have been changed for Mabel ! .... I must be Mabel, after all, and I shall have to go and live in that poky little house, and have next to no toys to play with and oh ! ever so many lessons to learn !  No, I've made up my mind about it; if I'm Mabel, I'll stay down here !" 

 

 

Charles Harrison Wallace