Just out of interest, since I've been Spunding via a capture keg, I've noticed that the capture keg ends up with 24-30 psi in it.
I've subsequently used that CO2 to purge kegs and pressurize the next batch. Would be interesting to use it to carb up future batches that I missed the pressure shut down time to have the primary carb, I might start saving a few kegs with just CO2 in them to see if there is enough volumes to do that.
JQ