A friend will be there in the afternoon and he always send me crowd updates. I’ve been to two or three DL anniversaries and I’ve never noticed a jump in crowds. I don’t think most people are aware of it, TBH.
As an aside, what’s nice about DL anniversaries at park open is that dozens (hundreds?) of CMs line Main Street as they wear large Mickey hands and offer to high-five any and all guests as they enter. On the 60th, there were free cupcakes but otherwise nothing special.