klipsch klipschorn date code???????

I would just like to know how a  serial #   8673283  for a klipschorn can be correct??

according to codes for this speaker the 86  is the year and the next two #'s = 73 is supposed to be the week the speaker was made.  am I missing something here?  I thought there were 52 weeks in a year.  so what happened here?  im looking at a pair and the #'s  are 8673283 & 8673281.