the top of my lungs

There should be a word for the date which isn't quite the anniversary of something but which is the nearest most representative date due to being on the same day of the week as the original event, if the day of the week of the original event is more or equally as pertinent than the date.

I tend not to study the armpits of T-shirts when I hang them out to dry, collect them from the clothes' horse, fish them out of a drawer or stuff them in my bag, but I spotted the decay of this one when removing it from my bag to put in the wash. I only do a big stretch once a day or so at work but shall try and remember to keep this item for home use from now on.