A while back and just out of curiosity, I had one of my 20lb BBQ tanks filled at Tractor's Supply and exchanged the 2nd tank at a Mini-Mart. When I got home, I weighed the two tanks on DW's bathroom scales. The TS tank weighed 3.6 lbs more than the exchanged tank.
I don't remember if the Mini-Mart tank stall states just how "full" the tanks are, but they ARE NOT Full.
2013 Silverado 2500 HD Duramax/Allison Tuned
Aviator Wright Flyer #1919
"First In, Last Out". 11B4Y
DAV, MOPH, VFW, 5/7 Cav,1/8 Cav Assoc.
11th ABN Pathfinder Co. N7MIP