There are a number of published photos of Dylan reportedly listening to acetates of Blonde On Blonde in a hotel room on the European leg of the tour. Some of these show discs with only two tracks on a side, clearly not corresponding to any of the sides of the released album. 

This is probably because most acetates were cut at 45 rpm, so would have a shorter recording time per side than a 33 rpm disc.  Furthermore the acetates were generally single-sided, so the whole album was probably spread across six or seven discs.