Myself, I'd try the longer of the two springs at least in one outing to see if it'll work and cycle and let the bolt hold open work when you're out of ammo.
You can always install it and while the upper is off press the buffer rearward with your finger first to check to make sure there's not too much tension. Don't expect the buffer to go all the way to the rear of the tube because it can't because the spring won't let it ride ALL the way back, but it should go at least about 2 inches or so deep fairly easily.
If the bolt stop does work when you're out of ammo, the longer of the two springs would be my preference because it would be more likely to help minimize the risk of bolt bounce if you're really chucking them off and would also slightly increase downrange velocity because the likely heavier (longer) spring will retard cycling and will keep the bolt closed a fraction of a second longer.
For the record, most carbine buffer springs are about 11-1/2 inches long, but many different sizes exist depending on who made the spring. Small variances (like an inch) wouldn't be enough to hurt anything and is pretty common as mentioned depending on who made the spring.
The most common thing to look for when using a slightly longer spring would be to pay attention to make sure the bolt holds open when your mag is out because too much forward pressure would likely cause carrier to ride over the stop and cause the mag spring to depress and not let it do its' job in holding the bolt in position when you're empty.
In a worse case scenario, using an A1/A2 spring may break the bolt stop tab, damage the tube or cause a bolt carrier to break, but I don't see it happening if the springs are only about an inch different in length.
If the longer of the two springs is around 14 inches long or more, then I doubt I would use either in the collapsible because that likely would be for an A1/A2 tube.
As for a reason why you got 2 different sized springs, I just don't know, but I'd be happy about it.
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