What is the correct reference for amount of salt in lacto-fermenting?
Simple answer

In general, when a recipe calls for "x tablespoons of salt per quart", you should add that amount of salt to a quart of water to make your brine.

The "correct" amount of salt

Salt in fermentation can vary wildly. As Sandor Katz notes in The Art of Fermentation (p. 99), "[s]ome traditions of fermenting vegetables, such as those of the Himalayas, mostly ferment vegetables without salt..." 

As (very) general guidelines:


less salt = faster fermentation and greater risk of unwelcome microbial activity
more salt = slower fermentation and lower risk


Factors like the size and cut of your vegetables, or the coarseness of your salt, could make an even bigger difference to overall saltiness than measuring your salt by brine vs. measuring by pickling container size.

So it really depends on the recipe, and on your own taste for salt (and risk).