CRT's that have not been used for many years seem to loose their emission. It's almost like the cathode gets covered in dirt & cobwebs!
Before starting a restoration, out of interest I usually hook the CRT up to the tester. Almost always they read zero, or very poor emission. If I'd have taken that at face value, I would not have proceeded with any restorations!!
Once the set is working well and the tube can be left with a picture, the emission often improves over several hours. If it doesn't, then I am quite happy to give the tube a gentle 'tickle' with the reactivator or failing that a full 'boost'
In all cases, my sets have ended up with perfectly watchable tubes.
My Sobell 1000 is a case in point. The emission read almost zero with the needle barely moving on the tester. It actually produced a perfectly watchable picture even without rejuvination- for 10 minutes that is until the LOPT went pop.....!
So I never worry about the CRT in the early stages because I know that the LOPT will give me way, way more aggravation!!
Cheers
Nick