Hi Dominic,
Thanks for raising an interesting question! To avoid any misunderstandings, I would like to share a small clarification.
The HDBaseT Alliance does not test all cables on the market – that would be an impossible task. Rather, cable vendors may choose to send in their cables for testing as part of our HDBaseT Recommended Cable Program or our Certification Program for Power over HDBaseT (PoH) cables. So if a particular cable that you are interested in does not appear on one of these lists, it means that the vendor did not choose to have it tested, and does not imply that it is better/worse than cables that do appear in the listings.
Good luck!
Daniel