There seems to be a big bug in utils.dateFormat, I have never noticed that before.
The year is wrong for 30.12. and 31.12. :
=>var vDate = new Date()
=>vDate
Tue Dec 31 09:25:26 CET 2024
=>utils.dateFormat(vDate,"YYMMdd");
251231
Same for 30.12.
I already created a ticket.