I went one more step... I believe it's at least four. As you'll see, for every four T206s, there are three Bitter's trade cards...
Based on the back cuts:
Nattress, Barbeau, Miller, Maddox cards were on line #1
Brashear, Rhodes, Rudolph (a), Schlafly, Barger, Graham, Bliss were on line #2
(no cards on line #3)
Rudolph (b) was on line #4