Errr. so it is. Sorry Mods, delete please.
[Note to self - Read twice before posting!]
Maybe a bit about it being even cheaper with an off-peak ticket Pad-Did but only on certain trains?
Yes, maybe I could have added more to the thread, Chris, but as I recall I was trying to explain a series of specific examples rather than give an overall explanation that got lost in a flood of "if"s and "however"s.
There is another section in my original post which suggest you travel offpeak if you can, and I think that sorta covers the extra bits your asking for ...