I certainly don't remember seeing gas tail lamps on trains in the late 1980's (Bardic MK2's were introduced in 1987, so they had been around for a fair while by then) but every train on the TVL seems to have gas lamps for some reason... which was kind of surprising. There could have been a few laying around, but hadn't BR fire regulations meant they'd all been replaced with battery tail lights by 1989? You certainly wouldn't want a gas lamp stuck on the back of a petrol, gas or oil tank wagon, if the TVL should ever get them in the future.
I remember some poor guard was either injured or killed attending to a tail lamp (which I thought was an oil lamp) and the general disbelief that such technology was still in use when there were, y'know, light bulbs. Can't remember when but it was genuinely surprising.
To paraphrase something I heard many years ago: "Don't start any vast complaints with only half-vast knowledge". And that applies to numerous whiners and nigglers on these forums and many others, to boot.