Ive also never heard of one going this long either. If this was me , Id be at the stage of "Wanting to know" ( hellooooo sleeeep)
Taz, Ive witnessed many threads on preg mares over the years. Theres been a couple I've wanted to throw my keyboard thru the computer screen. Owners of pregnant mares that have been so blasé about their mares pregnancies. One in particular with a mare that was so overweight she could not actually deliver the foal. She was warned and didn't listen & then got nasty when her mare and foal didn't make it.
Reason I have written the above is because I really want you to know what an amazing job you are doing
You are attentive, caring & doing everything you can to get this foal safely on the ground. And most of all , this is all on sleep deprivation. I know you are most likely exhausted but keep going , your doing awesome