Hi Andy
Thats more or less it, taking a simple example of a S. flava, then a flava crossed with another flava is still a flava even though in theory its genes are now different, this also applies if it is selfed, but you cross it with something else then it becomes a hybrid, flava x leucophylla = S. X moorei, and flava x purpurea = S. X catesbaei, and it will remain so if you backcross it with one of its parents, i.e S. catesbaei X S. purpurea = S. X catesbaei.
Similarly if you cross a sub-species with another sub-species, say a var. flava x flava rugelli, then you still have a flava, but now a hybrid flava as it is now neither a pure flava or rugelii, having a mix of the genes of each parent. This is why it is important to keep good labeling, so don't label it just as a flava, as this flava will tend to exhibit the predominant genes of one of the parents, so may look a lot like a rugelii, and with subsequent crossing, the genes of the other parent can/will come out and totally cock up someone's breeding programme.
Hope that makes sense, it's a poor explanation but I hope you get the gist. Barry Rice does a nice beginner's introduction have a look at this.
https://www.sarracenia.com/faq/faq5547.html
And if you want to explore a bit try
http://www.johnjearrard.co.uk/plants/sa ... plain.html
Cheers
Steve