Shouldn't revisions sprout from a single text authority?

I was just looking at John Dalles' hymns in the database and noticed there were two listings for "Come, O Spirit, with your sound", one called "come_o_spirit", 1983, in the 1990 Presbyterian Hymnal, the other called "come_o_spirit_with_your_sound", rev. 1993, in the 1995 New Century Hymnal.

I'm thinking I should combine these text authorities, but I'm not sure I know how to go about it so as not to destroy critical evidence. Although the New Century is known for its sometimes startling, even extreme emendations of texts, I find it hard to believe that this one was modified enough to make it essentially a different hymn.