Reversing Hum URLs

I’m getting some 404s errors, and I’m trying to reverse the Hum URL. However, using TanTek’s grid (tantek / NewBase60 (pbworks.com)) and Chris Burnell’s calculator (NewBase60 Calculator · Chris Burnell) to verify, I’m not getting anywhere that makes sense. 4vn = 2018 August 3 (I think), but this site wasn’t active then, and the earliest post is 2018 Nov 29 (whose Hum URL is 1J3 which equals Oct 27 1982).

I readily grant that the whole newbase60 is beyond me and that I could well be doing something wrong.

The page I need help with: [log in to see the link]