8 note scales in Baroque music?

Yes you read that correctly. I have come across two examples of the use of 8 notes in pieces from the baroque period and wondered if anyone else has noticed such things? True, it could be described in many ways, passing notes, harmonic extensions or whatever but the key is that the music has a harmony which includes 2 notes on the same degree of the scale and not merely an harmonic equivalent.

For example, Bach Sinfonia no. 2 in C minor, BWV 788, bar 19: Db held over in the treble clef but while that is ringing the bass clef is playing D natural. It works wonderfully but I am working to understand why the D in the left hand is not Db too. I can see the modulation to F Harmonic minor but the addition of the D natural in the music means it is either F Melodic with a b6 or F Harmonic minor with a natural 6. Either way, the formula is 1 2 b3 4 5 b6 6 7. The same phenomenon occurs in another piece but I'll wait and see if anyone else has any other examples to contribute first. See score below: