There are people making that claim, specifically ballots being sent back that weren't initially dispersed.
The best thing to do to clear this all up is to go right to the source. Check the AZ Senate hearing transcript from several days ago to find out what they are claiming.
I haven't had time to do that yet, but I will get to it.
I'm pretty sure they're saying there were 74K more ballots received than were mailed out.
The auditors said that they have roughly 74,000 EV33 ‘receipt forms’, that do not correspond to EV32 ‘sent forms’, and for that, they need an explanation in order to proceed.