These SLC▸ 's really aren't ever set in stone anyway and I predict several amendments before this current version is actually initiated.
It is the 3a SLC that was refered to anyway. I believe this is the one that would apply had the AT300 order for Plymouth/Penzance services not gone ahead. I don't think SLC3b (which I think is the AT300 timetable from Dec 2018) has been released yet.