You've answered your own question here. If you passed an ATPL check ride then it's not converted from anything and you are good to go.
A lot of people get confused by the word 'convert'
If you hold a CAA ATPL and go to Canada to 'convert' to TCCA - you need to meet medical, written, experience etc and take a flight test. You might say that you 'converted to TCCA' - but you haven't actually comverted anything - you met the requirements and you hold a full TCCA ATPL.
What the FAA don't want to see is anything with the restriction "only valid when accompanied by UK licence no ####" or words to a similar effect. That is because they themselves issue part 61.75 certificates which are based on a foreign licence. Otherwise known as OTBO or piggyback licences.