The point of the chart is to get the chanter in tune. Traditional smallpipes play at a nominal pitch of "F" but just where that F is in relation to concert pitch (A=440) depends on how the maker set the set up. Some makers in the past have not cared about the set playing at exactly concert F but somewhere close and often a bit sharp. The main thing was to get the set in tune with its self so that all the notes were in the correct relationship. Imagine it is like a guitar in the days before electronic tuners when you set one string in tune till it sounded about right and tuned all the other strings to it. and all the other instruments in the band would then tune to the guitar. The group could easily be a semitone away from concert pitch.
My choice was to go for Concert F then I could play with any fixed pitch instrument. It is more demanding to make a set play exactly in tune at concert pitch regardless if it is a G set or a traditional F set. The problem with the F & a bit tuning is that there is no universal agreement on how much the "& a bit" is.
It is impossible to force a standard pitch. It seems to be almost a religion to stick to a local pitch. Of course as soon as the pipes are used in a band setting with fixed pitch instruments all the F and a bit nonsense goes out of the window and concert pitch rules regardless of local sensibilities. Note that by concert pitch I mean any note that is related to A=440