Why the numbers you already have are not enough
Every channel business measures dispatch accurately, because dispatch produces an invoice and finance needs it to close the books. The number that actually predicts next quarter, though, is what left the retailer shelf. When those two move together, the channel is healthy. When dispatch keeps rising and offtake flattens, you are financing inventory that will come back as returns, discount demands or an unexplained order holiday.
The honest position is that most secondary sales data starts out poor. Outlet names are inconsistent, quantities are rounded, and a chunk of it is entered on the last day of the month by someone catching up. That is not a reason to skip it. It is a reason to design collection so that the easiest path also produces the cleanest record, and to treat the first quarter as calibration rather than judgement.