My Calendar Part 1 - The 3 season year.

Well spotted, Mark At least you read it!!
I tried the one seed a week experiment once...........the answer's NO................but this leads me on nicely to My Calendar Part 2 - the 13 month year when you sow the same seeds (almost) every 4th week of the year.
Week 1 I sow Root veg
Week 2 - Shoots like Alliums
Week 3 - Fruits - peas, beans, tomatoes etc
Week 4 - Leaves - brassicas and lettuce .

So for a succession of cabbages you sow a few every 4 weeks - obviously changing the varieties to match the seasons.

This is what I try to do - but usually fail miserably because I forget - although my computer diary reminds me every day which week it is - this week is Fruits and I plant to sow some DFBs and dwarf peas for the GH and some Wizard Field Beans for outdoors. Going to experiment with a late sowing of courgettes and cucumbers too, just to see if its possible to sow this late.

This is almost a moon gardening calendar, except starting with the New Moon it would be:

Week 1 - Leaves and shoots
Week 2 - Fruits and flowers
Week 3 - Roots
Week 4 - no sowing

Like you I often end up sowing in the "wrong" week because life is never that tidy, but having it as a framework brings some order to the chaos of gardening!