The tip to tip measurement is recorded for the purpose of making it easy for the office to visualize whether or not the main beams (as viewed from above the tines) are heart shaped, or V shaped.
Heart shaped i.e. - inside spread = 16 0/8. Tip to Tip = 4 0/8
V-shaped i.e. - inside spread = 16 0/8. Tip to Tip = 16 0/8
Basically the tip tip measurement and the inside spread is one and the same.
It does happen more than you might think.
-Scarne
P/Y measurer from way back before there were cell phones...