The question I have is this - is the test ID generated when the test results are generated for the first time (either sent by email if they have it, or accessed through eGov or eHealth portal), or are they generated as soon as test results are complete? If it's the former, then it's theoretically possible that the first (positive) results have been downloaded for the first time on Dec 26, and thus have a higher ID number.
Unfortunately, no data points from me, even though I have been tested MANY times due to my profession. They've got my email, so they obviously get generated immediately.
However, I do have a data point for screenshots when QR code of the positive test stated that the result was negative. This is something that happened to me as well (back in 2020, once, and never since then). It was a bug, obviously. The second part of the ID is person-specific (all my test results have that second part identical, regardless of when they were taken) - it seems that if a positive test is followed by a negative test, that happens sometimes.