Ok I will add the new bag which would make total of 80lbs of salt in the tank and start the regen.1. I would add the second bag now. I would pour it into a corner, which will let some salt be above water for the next few regens.
2. Do not manually bypass the softener during regen. If you did that, the softener would not get water needed to regen. The softener itself will bypass water around itself during the regen, in case you want to flush a toilet.
If you have not done a recent regen, that is good from a troubleshooting point of view. Yea, I would expect that resin to be long depleted of softening ability. So no salt for months could explain hardness all on its own.
Is it ok If i use the water while its regening?