.
...FWIW, I ordered a bulk batch of 8 Continental tubes, unboxed (so cheaper) a few months back. They were not advertised as sealant filled, but the first four I installed all had defective Presta valves. I could overpressure the pump to get air going into them, but there was no way to let air out without removing the valve core. The 4 unused ones, I returned, but the installed tubes I decided to try fixing with new valve cores, bought in a package of 20, also on Amazon.
This worked fine, and I didn't have to go to all the work of removing the defective tubes and replacing them, so easier.
I've been buying Conti tubes in bulk, and using them for years, and this is the first time I've had a problem with them.
__________________