Many thanks to those of you who figured this one out! I have been tearing my hair out for WEEKS trying to toggle the date complication back on, on multiple different watch faces. Never in my wildest dreams did I imagine that Apple would force their crummy iOS calendar on us just to make the watch function to its fullest, but you all were quite right; as soon as I reinstalled it, the date complication was immediately available! Most sincerely, thank you to those of you who took the time to figure this out. This little Apple/Mac ****** is most appreciative.