The start date of counting period for permits

Hi all,

I am planning to apply for single permit with an indefinite duration (in Flanders), as I am close to finish my fourth year in Belgium (without a gap in employment). Do you know which date is considered as the start date for counting these years? I mean, is it my first work day in Belgium, or the date in my first A card, or sth else?

For instance:

• 30 September 2019: First work day in Belgium (while staying at a hotel)
• 6 November 2019: The date when the first A card was issued

I am  trying to understand when I will be eligible to apply. If it is the date of my first A card, should I also wait until end of November (to include November's paycheck in my application file as well)?

Thanks!