there is no indication of 'frozen' ATPL status on the licence. When applying for jobs most airlines will request a copy of your MCC certificate, which you get upon course completion from the FTO - the CAA also retain a copy of it. For the theory part the CAA have a record of all ATPL theory exams undertaken and the results obtained, the candidate also has a copy of the results should they ever need to 'prove' that they have studied at ATPL level.