I have a Zenith SMS1917SG "Sentry 2" 19-inch table model TV, built in 1995. I must have been extremely fortunate to have gotten a set with a good CRT, as this TV still makes as good a picture today as when it was new, over twenty years ago.
One reason my set is still working well with its original tube, however, may be that I only used the set as a daily watcher for about four years, after which time I bought an RCA 19" table set and put the Zenith in storage; I do not use the Zenith set much anymore since buying a flat screen five years ago.
It could very well be that the 1990s Zenith TVs which had all the CRT problems were heavily used, or else the SMS1917SG and other Sentry 2 sets of the same model, as I said, may have been shipped with a "good" tube that did not short (if there actually was such a thing, which I doubt; from what I have read about those tubes, including your observation, they were bad news almost from the beginning). When the CRTs shorted in these TVs the damage (so I have read in Zenith forums elsewhere on the Web) was extreme, including destroying the entire video output system, if not the power supply and other parts of the set as well.
I wonder if the "Zenith" branded flat screen sets, made by LG, were just as bad from a quality standpoint. Since these TVs were not made by Zenith (which was long out of business by this time), I doubt the FPs had bad LCD panels. Of course, I am referring to flat screens made by LG just after the DTV transition; today's LG sets may be much more reliable than the post-Zenith ones.