Yes, you're remembering right, Eric. Of all of the commonly played positions in standard tuning used by Country Blues guitarists, D has the highest-pitched lowest root, if that makes sense, the open fourth string, D. If you routinely do an alternating bass hitting the root of the chord on beats one and three and the third or fifth of the chord on beats two and four, alternating bass towards treble, that means in your I chord in D position you'd essentially be playing a four-string guitar, and missing the fifth and sixth strings altogether.
Of course, most players who played in D position in standard tuning, got around that limitation by choosing to voice the bass in the D chord differently, with Scrapper Blackwell doing a thumb wrap at the second fret of the sixth string, John Hurt playing his alternating bass in D as a V-I alternation from the open fifth string to the open fourth string. One person who used an inventive work-around was Rev. Davis, who essentially played in D using a C shape to do so, so that he could hit the root on the fifth fret of the fifth string and alternate to the third at the fourth fret of the fourth string.
I sure wish Lemon, in particular, had recorded some tunes in D position in standard tuning because I would have loved to have seen and heard how he would have gone about that.
All best,
Johnm
