It's the other way round, isn't it??!
If you pick an unbraced bow off the rack, and it's bent towards the belly the amount it's bent away from a dead straight line is string follow, because that's how much it's following the string. The original stave shape is irrelevant, as it's just a way of describing the shape of the bow, i.e. "it HAS string follow".
Set requires the original stave shape to be known, because set is how far it's bent towards the belly from its original shape due to cell compressjon, i.e. "it's TAKEN set".
You can have a bow with 0" of string follow but 2" of set if the original stave had 2" of reflex but the bow is now dead straight.
You can have a bow with 2" of string follow and 0" of set if the original stave started with 2" of deflex.
You can have a bow with 2" of string follow and 4" of set if the original stave had 2" of reflex and the bow now bends towards the belly 2" from dead straight.
This means that set is the temporary factor, because the cell compression can ease back again after not being used. String follow is a permanent shape to a bow, whether it's just been shot or hasn't been touched for years.
Right?!