From the 2 July 2019 FAQ of www.W5SWL.com
Rest assured, for our brand of connectors (by W5SWL) that are applicable, we have performed RL (Return Loss testing), insertion loss testing, power testing (to the extent of our capabilities), frequency max, physical make up and usability, etc when we accepted a design and we do continued spot testing as a routine in our well equipped test room. We test against some very popular brand names in the high tech industry to establish what we call good and normal specs.
While we certainly know the specs of our connectors the reason we don't publish them is that we offer our brand line of connectors at a low consumer grade price level. We don't publish specs since we would have to increase pricing just to chase specs and small variations. Our original goal and decision was to offer consumer pricing levels even though our connectors meet very suitable specs and could easily meet higher price levels.
We have done connectors long enough to know, as our many and wide range of customers* know as well, that our line of connectors perform quite well and at a affordable price structure. Try one of our brand of connectors, we are easy to get along with should one of our brand of connectors not work to your satisfaction.
*Ham and hobbyist users, US Mil and the Coast Guard, Government (US 3 letter agencies, state, county and local) as well as independent radio shops and equipment manufacturers to name a few.