Hoggy
The lumps can be installed in any Head at any point.Fresh, Used, stock valves,Bigger, Or other wise. (Other Then a Broken one unless for testing reasons)
Bottom line is a Bolt in Lump can be done at any point or at any faze. Where as a Braze in Lump can Only be done If there hasn't Been any Port work done.
#1 reason is It runs a Much higher risk of cracking a Head.