Hi Luftwaffle,
That section specifically enables the admin. week (actually, an admin. fortnight).
It says (quoting from memory)
"A pilot shall not fly, and an operator shall not roster a pilot to fly, where at the completion of the flight the pilot will have accrued more than 90 hrs duty in any fortnight period standing alone. The operator may specify the day on which the fortnight commences."
There is a clear distinction between how this paragraph is written compared to other paragraphs above it (below it?) that use phrases similar to:
"...may not accrue more than xxx hrs flight time in the previous 7 days..."
Ditto for the paragraphs concerning 30 & 365 day FTL.