Data source used?

Hi,
(Part of the reason for this post is to retest my email access.
Apologies in advance...)

I came across this site
   https://quadrature.co/work/classified-orbits/
along with a companion page
   https://quadrature.co/work/unknown/
each of which reference unknown/classified objects in orbit, as tracked
by amateurs.

I'm wondering if anyone knows the source of the data used?  One
reference is to a dataset of 450 items,
but the McCants file has less than 200 if I read everything correctly.
I've sent an email but not received a reply.

TIA,
Matt Considine
Vermont, USA

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