all of this is based on Internet research (on the quest to find C99 seeds for me and my girl).
Sub has a sticky on the process of cubing. I believe this was the beginning of the C99 breeding project.
mother plant was suppossedly a Jack herer f2, or an f1 between a jack herer female x unknown. she was dubbed princess.
they then outcrossed to shiva skunk male (northern lights x skunk 1) to achieve P.50 (50% princess).
Those subsequent seeds were grown out and a male selection occurred. I dont know if they selected a single male or went for the mixed bag of pollen approach, dunno if anyone does. This male P.50 were then bred back with Princess to create P.75 (p50 x princess = 75% princess)
same deal again this time, p75 crossed back to princess after male selection to create p.88.
selection again, cross back to princess (if you cant tell I'm getting more stoned as I type) get p94. they decided princess 94 was a lame name, so they changed the 94 to 99 to sound more badass and called it cinderella.
none of these original p88xprincess seeds are available, but there is a wide selection of cindy 99 f2s around. although they mayhaps show more variation than the original stock, the whole goal of Interbreeding is to produce a true breeding, low variation strain, which leads me to believe the f2s are probably pretty good. This also supports why space queen has proven to be such a stellar breeder for sub, although genetics of romulan (and no personal experience with its pheno variation) is unknown, c99 provides a sold backbone for the cross.
edit*
there are also seemingly loads of P.88 seeds still out there. forum member guile is one who has those.