Can depletion data show if my marketing worked?
The short answer: It can show whether accounts bought more after a campaign, which is a useful signal. On its own it can't prove the campaign caused it, because holidays, pricing, distributor programs and stock levels move orders too. Comparing against similar markets or accounts that didn't get the campaign makes the read much stronger.
Decide what "worked" means
Website visits, a new account, a reorder, or more cases in a market are different outcomes at different stages. Pick the one the campaign was meant to move before it starts.
Write down what you did
Campaign dates, where it ran, which products, what it cost, and anything else going on at the same time, like a distributor program or a price change.
Compare fairly
If orders went up in the market where you ran ads, look at a similar market where you didn't, over the same weeks. If both went up the same amount, it probably wasn't the ads. If only yours moved, you've got something.
The same works at the account level: compare accounts that got the push with similar accounts that didn't.
Keep the levels separate
Clicks and impressions are attention. Inquiries and demos are interest. Account orders and profit are sales. Report each one as what it is and don't let one stand in for another.
Use it to pick the next test
Decide whether to repeat, adjust or drop the activity based on what you saw. A good write-up says what happened, what you can reasonably conclude, and what you'd test next.