I had tried this site a year or two ago and found it unusable then, but it seems greatly improved now. I found posts as old as 1982, but recent coverage seems to stop around April 2022. Crucially, it supports full-text search on posts within a specific group - something which my own site https://newsgrouper.org cannot do. I find the user interface a little awkward, but it does now appear to be a really useful resource.