Not sure why this post is in the Video Processors forum, but they can be revivied I believe. There is a company called VDC if I remember correctly which can "retube" tubes. You might try searching the CRT projectors forum. Curt Palme might be the right person to ask about this - he does a lot of CRT repair/reworking/etc. and would probably know.
I do not think that projection CRT tubes are re-used. They are small enough that there is little or no cost savings in re-using them.
Long ago, the glass of large CRT's was re-used. The primary item that needed replacement was the electron gun in the neck. The phosphors were or were not re-poured in black and white tubes depending on condition. For color tubes burned phosphors or warped shadow masks forced the tubes to be discarded, since re-doing those components is an expensive proposition.
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