https://web.archive.org (take a screenshot option if you have a login and it's JS madness WBM can't handle), https://archive.ph, etc (hopefully captured more than one if possible) - random screenshots are proof of absolutely nothing.
Also because xitter provides a broader discussion platform and reach compared to only HN (even though I highly appreciate the HN content). But yeah, the xitter post should preferably also contain that url to the source.