The parallel sequence of glyphs evidently starts earlier - see Sa5-403--409.
Bb4-14 Bb4-15 Bb4-16 Bb4-17 Bb4-18 Bb4-19
Sa5-410 Sa5-411 Sa5-412 Sa5-413 Sa5-414 Sa5-415
Bb4-20 Bb4-21 Bb4-22 Bb4-23 Bb4-24 Bb4-25
-
Sa5-416 Sa5-417 Sa5-418 Sa5-419 Sa5-420