Leland,
I can't really offer much insight on contemporary hymnals. I buy some and skim through them at times, but you don't really notice things doing that the same as when you sing from a book.
I expect that there has always been some variation as to how typesetters resolved these issues. For the most part The Sacred Harp uses texts that are metrically consistent without variation from stanza to stanza. One that is not that comes to mind quickly is THE MIDNIGHT CRY.
For example, the fifth measure has two quarter notes, but to resolve the extra syllable in the text we [at least we here] sing "Ne-glect" as if there were two eighth notes there. (I think you have to do that on some of the other stanzas, too.)
SWEET MORNING in the 1860 Sacred Harp book shows the inconsistency of a typesetter within one song on one page, sometimes beaming the eighths and sometimes using a tie/slur.
I don't have my Cooper Book with me at the moment, but two songs in it that you might look at to see how such is resolved in a most recent typesetting of a Sacred Harp book are LITTLE PILGRIM (392, which has a second stanza added that isn't exactly consistent with the first) and LONG AGO, COMRADES (582) which has several irregularities in the text from stanza to stanza. I think THE ORPHAN GIRL (506) also has an irregular text that isn't consistent from stanza to stanza.
On the general beaming issue, I think THE PROMISED LAND can provide a good example of the tied eighths where there is one syllable and not tied where there are two.
In this song the seventh and eighth measures in the top brace are the same as the sixth and seventh measures in the lower brace (except one typo). In the upper brace where one syllable is sung with two notes, the notes are beamed together, but in the lower brace where two syllable are sung with two notes, the notes are not beamed together.