No, it is not extra air. It is part of your basic air supply that you set aside as a reserve for your ascent. All the J-valve does is alert you that you now need your reserve, and (when pulled down) gives you access to that reserve.
No, I would not have gone to 100 ft with a J-valve unless it had been st to a higher break pressure.
FYI, here is how much gas you need to get to the surface, for an RMV of 0.7 cuft/min, from various depths, for yesterday (60 ft/min and no safety stop) vs today (30 ft/min with a 3 min safety stop). The 450 psi needed from 130 ft, and getting back with 500 pis still in the tank, is where the "leave the bottom at 1000 psi" comes from. All this presumes an AL 80, and no panic.
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