WHV->WP In-Country Application --> ILR Start Date?

I had entered UK as WHV in 2002 and obtained the in-country WP in Sept 04. The label "Resident Permit" on passport has the "Date of Issue" as 20 Sept 04 but I did not travel and re-enter UK using the passport until Nov 04 so there is a stamp on the resident permit label dated 17 Nov 2004. So my ILR clock starts 20 Sept 04 or from the re-entry date 17 Nov 2004? If it is 20 Sept 04, then for the 28-day rule, which date can I go to PEO to apply ILR? 23, 24 or 25th Aug 09?

Many thanks!