[BryantD]

Note https://archive.org/details/usenet?tab=collection -- I haven't reviewed it so I don't have a take on how complete it is, but the archive team there tends to be fairly completist.

[iggldiggl]

uk.railway archives from that collection only go back into the early 2000s, whereas I know Google had posts going back into the 90s. (But unfortunately Google is currently blocking access on account of too much spam, maybe facilitated by Google Groups in the first place…)