Shooting spines that should be too light?

[30coupe]

One of the problems with charts is, as has been mentioned, different brands or even different models within a brand often spine stiffer or weaker than marked. I have some .500 Nuge (Gold Tip) blems from Big Jim and some Beman ICS Bowhunter .500s. I have to leave the GT shafts about 1/2" longer than the Bemans with the same point weight and fletching. Nothing wrong with either shaft, but there is always some variation, so I just start long with a new batch and whittle them down until they behave because I pretty much know how much point weight I want to use.

Sounds like you have found your sweet spot, so no need to over think it.