Yes... Date. That is the only one that ever worked for me.
I also struggled with other tag blocks, mainly XMP, with a zero strike rate there too.
I don't fully understand how EXIF works, but like you, I looked for the the EXIF names in various places and found that MC, AcdSee and XnView all displayed the labels for some exif data slightly differently, leading me to believe that the actual tag labels in the file were not user friendly and were mapped somehow by the various different software options, translating them into their own definition of tag label.
A simple one like "Lens" simply refused to populate using Tag(), and I tried all case variations. I decided that I would never know how lens was labelled in the EXIF block and gave up on it. MC now populates the Lens info on import and I've never tried using Tag() since then, and 'then' was many years ago.
Is there a specific value you're after, or is it just general curiosity/frustration with tag() that you want to put to bed?