How do we ask about gaps in teaching after several teacher changes without blaming the current teacher?

Our new teacher opened the textbook at the next unit. Several of us said we hadn't finished the previous one. Two students said their last class had covered it. We had been split between different temporary groups for three weeks.

The end-of-term assessment is still on the timetable. The new teacher asked us to revise the earlier material independently and bring questions. I can work through some of it, but I don't know which parts our different groups missed or whether the assessment assumes we were all taught the same sequence.

A parent wants to complain that the new teacher is refusing to catch us up. I don't think she yet has a clear record of what each group covered. What would be useful for us to bring to her or the course lead now? I want an agreed plan for the missing material, rather than a list of people to blame for a timetable none of us chose.