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As for check pilots, they are Captains (4 stripes) who are also check pilots (training captains, examiners, etc.). They still only wear 4 stripes.
Everyone up front should have at least 2 stripes I think.
However, those stripes might only be on their jackets not on their shirts, depends on the company uniform rules.
All pilots of commercial airliners have to have at least a Commercial Pilots Licence. The "upgrade" to Airline Transport Pilots licence, in the UK, involves completing 1500 hours of flying time and doing higher level of exams than at CPL. However, most new pilots since a couple of years ago, take their exams at ATPL level from the outset, which means they have a CPL and a "frozen" ATPL. They have exactly the same licence as someone with a full ATPL but not the total flying hours.
Why do you ask?