EOTD is something some people spend and inordinate amount of time worrying about something that doesn't affect 99.99% of CO2 users.
It is caused by "cheaper" regulators loosing regulation when CO2 tank pressure drops and releasing the rest of the cylinder uncontrollably into the tank, generally making the fish suffer.
Some regulators are not actually regulators, but in the "gas world" are flow controllers and are either pin holes in a metal diaphragm or a metal sponge, as pressure drops diaphragm bends and metal sponge opens a bit releasing rest of gas. Generally not a problem when used with disposable CO2 containers as in use for welding you get notification due to gas rushing out that cylinder is empty and not a problem for fish as dump volume is quite small. Major issues of course if using a 2Kg of bigger CO2 source as dump volume can be large.
Regulators like this below designed for disposable containers, so EOTD is not an issue.
A dual stage (as opposed to dual gauge) does not suffer from EOTD as first regulator drops the 55bar tank pressure to say 10bar and second stage drops pressure to 3bar. The output maintains 3bar as the tank pressure drops from 55bar to 10bar as it starts to go empty. Does not EOTD.
A single stage regulator (cheaper) drops the pressure straight from 55bar to 3 bar and can suffer falling pressure as tank pressure drops, or if you have a cheap regulator may suffer EOTD. My Co2Supermarket regulator starts to drop pressure ie fall in bubble rate when pressure starts dropping. This goes on an for a couple of days and I just change the cylinder. Have watched it drop to zero bubble rate (10bar cylinder pressure) and no EOTD for me.
Please note the pressure in CO2 cylinder (unlike an air cylinder) is roughly constant (55bar) regardless of the cylinder contents as the CO2 is liquid. So you can't reliably work out how much is in the cylinder based on pressure. Hint use a set of scales, a full 2Kg FE is 2Kg heavier than an empty one.
. Once all the liquid has gone, only gas is left and it is then the cylinder pressure starts dropping.