At GRSP the standby hunters also have a potential of qualifying for the other nearby location too...or at least did years ago the last time I got drawn for GRSP and went thru the Hunters Talk with the other place's hunters too.
Can't say about Gvt Canyon, but with it's proximity to the SA Metro area..I'd doubt there will be any SB's anymore anywhere down there within 100 miles of SA, especially with the advent of the 2nd Drawing available to TPW's Hunt planners.
I'd get lots more miles away from SA or Austin to look for a Stand By opportunity....and rather than waste myu time on the road, I'd let my fingers do the walking and spend time on the phone talking to SP/WMA Mgr's the week before the Hunt Date & I made the trip.
JMHO & YMMV
Remember Aesops Fables outcome of the "Scorpion & and the Frog's" crossing the river when they get to other side
a LOT of Money doan't buy you ANY Class..old South Oak Cliff mantra
Those who fail to learn from History are doomed to repeat it...Santayana