We have the term "Lord's Day" in Rev 1
We have "The Son of Man is LORD of the Sabbath" in Mark 2
We have "the Sabbath - the Holy Day of the LORD" in Is 58:13
But to your point - we don't have any other text that speaks to the Rev 1 term.
So then do you view Is 58:13 as a mistake?
13 “If, because of the Sabbath, you restrain your foot
From doing as you wish on My holy day,
And call the Sabbath a pleasure, and the holy day of the Lord honorable,
And honor it, desisting from your own ways,
From seeking your own pleasure
And speaking your own word,
That Is 58:13 text may help explain why there is such agreement between Sabbath keeping and non-Sabbath keeping scholarship that "The Lord's day" in the Bible - in the OT was the 7th day Sabbath up until the cross (At which point the two groups differ in their views).
I agree that outside of the concept of "my holy day" and "the holy day of the lord" there is also the day of God's wrath and vengeance (a future event) called "The day of the Lord"
3 Know this first
of all, that in the last days mockers will come with
their mocking, following after their own lusts, 4 and saying, “Where is the promise of His coming? For
ever since the fathers fell asleep, all things continue just as
they were from the beginning of creation.”...
10 But
the day of the Lord will come like a thief, in which the heavens will pass away with a roar and the elements will be destroyed with intense heat, and
the earth and its works will be burned up.