Oh, yes… I could notice a difference. I control my HH with a normal whole blood donation (around 470ml).
My best estimation (without back to back ramp testing) is that I lose about 6% of my FTP right after my donations. Heart rate and RPE are both elevated at the “old” power efforts, pretty much across the board.
So I just make a manual adjustment to my FTP after each donation (assuming I am not testing right away) and roll with that to start. I still adjust a bit as needed, like any other time. But that seems like a decent starting point for me so I am not overcooking my efforts after the donation.