Ann: Southern Cooper Basin Gas Project - Operations Update, page-19

No I'm saying what's known as the Critical Desorption Pressure (when they START to release gas) is probably around 1000-1500 psi, depending on the shape of the isotherm. The gas they've seen so far is probably mostly from coals near the wellbore that have been depressurised due to pumping to below the CDP, but the average reservoir pressure at LC is only 2400 psi as reported in the ann. That's still above CDP if the saturation is 90%. So most of the coals are not desorbing gas yet - only the coals near the well.

Once they hit desorption pressure, for each psi they drop further, the amount of gas released will increase exponentially. The reference by STX to 500 psi I believe represents the inflection point of the isotherm, or the "elbow" of the curve where it starts to really ramp up. Above 500 psi, it takes a large drop in pressure to get a relatively small release of gas from the coals. Below 500 psi you only need a small drop in pressure to get a large release of gas.

I might try and post an image later to help explain it.