Would that have been my listing by any chance? I bought a load of used ones bulk and matched them up, were some very nice tubes in there.
From what i've learned so far, all the silver shields seem to sound the same to me, but i haven't heard the elusive 1975 silver shields yet.
I have a pair of 1978 with the long silver shield, and they seem to sound the same as silver shields from the early 80's but they aren't very well matched, but i keep them for myself because it's not a big issue for me to shift the balance left or right one notch in my soundcards control panel.
I've had a load of the long grey shields from the 70's, including a pair from 1975, can't say i was blown away to be honest, very good tube but i think the bass was not as tight as the silver shields, don't get me wrong they are a fantastic tube, just not the presentation that pairs well with all my gear.
Short grey shields from the 90's - 2000's i thought were completely un-remarkable, i thought there was a bit of harshness in the treble, and maybe a bit too much bass, bit of a V shape going on, some people might like it but it wasn't for me.
Take all this with a pinch of salt because the tubes were well used and only a small batch, might be some years in between that sound great and go against the grain of what i'm saying.
I've bought another load, 28 more tubes which i should have end of next week maybe, will have to wait and see what goodies i have in there, so i might be revising my impressions.