Oh well, looks like somebody noticed
Let's say that the previous numbering (week_number-VPS_within_the_week) has been "reinterpretted" as (bigger_update_number-smaller_update_since_the_bigger_one), i.e. the first number isn't really the week number anymore.
Actually, what I wrote is not even fully right... it's not necessarily a "bigger update" - the thing is that the differences (in the differential updates) are transfered between the current VPS and the previous XXX-0 one (i.e. not the previous one if it doesn't end with a zero). So, the more XXX-0 VPS files we release, the smaller the differences, and the smaller the traffic.
The numbering will probably return to "normal" when this year is over.