But this would mean the epoch here would be the 2 April 1984 or maybe the 1st, if you respect the time as well, which sounds a tiny bit random lol. But so would be to use a week counter in the first place :D Especially since those trains are from the early 2000s.
How did you get to that epoch? I haven't seen any images of this happening earlier than 2003, so the overflow must have happened late last year or early this year, and whatever week 0 is is some time around 2002/2003. That would also fit with your comment that they were introduced in the early 2000s.
Maybe they just didn't expect the trains to last 20 years 😄
It could be that the epoch is the start of 2003, so any train with a reset week counter shows 2003, and now they all do since the counter has overflowed late last year.
The fact that they use a week counter in general is something I remember from someone familiar with the onboard computer system, but I don't remember how it's set up specifically unfortunately.