Thank you. I'd say that is very convincing, especially with him walking about on 16, 17th and 18th.
When scanning a QR code, is the date visible anywhere on the page? I am trying to guess whether someone just edited a PDF with a different date (might explain why they chose 16.12 - you need to change a single number). Alternative would require someone back dating a test in the system.
No, that is the weak point of this system. Anyone can change date in pdf and no one can check that except Serbian authorities. The only limit for date is one year after test because verification system (qr code link) is set not to validate older tests.
Only outlier is Djokovic's positive test. It perfectly fits to 26. December, the same date timestamp was created.