Yesterday I went to our church to practice 4 pieces from Buxheimer Organ Book. This is the German music collection written in the middle of the 15th century, approximately when Christopher Columbus was born, 600 years ago.
The pieces in my edition where written in 3 staves but the lowest stave wasn't supposed to be played with pedals. I had to play the two lowest parts with the left hand.
The problem is that in the 15th century, it was quite common for voices to cross each other which means that the lowest part can go higher than the middle part.
It makes reading such a score quite a burden.
What helped me was to slow down my practice tempo significantly and play the resulting three-note chords one by one, almost without the rhythm.
In other words, I had to make sure I don't press the next notes without being 100 % certain the notes will be correct. It's only possible in extremely slow tempo.
See if this helps you, if you ever have to play music with voice crossing.