The number on the package is the nominal strength of the line. Much like how the cross section of a 2x4 doesn't measure 2" x 4" or how 1" pipe varies slightly in diameter, but is designed to be able to be interused with different manufacturers fixtures and not create fitting problems. The manufacturer determines the rating on the package by whatever applications they think will best match up with that line product in terms of diameter and actual strength. This is a much stupider way than the PE system which standardizes diameter and then provides ABS for each product, but the American consumer is by and large too stupid to figure this out. The strength-to-diameter ratio of braid is so high that as the thickness changes along the length the strength also changes significantly, and is much more prone to significant strength reductions in defects. Higher quality line can/does translate into stronger line on the whole for a given diameter when production is tightly controlled. The trade-off is generally process cost and cost from losses of rejected product.