Identify and add new line of information based on newly added data in another sheet

Good afternoon, I have no idea if this is even remotely possible, but it beats me manually checking all of our customers each time they do a new order.

So we have 300 ish customers and around 130 items that they can purchase. I was making a sheet that had all of our customers and item codes and then vlookuped off our previous 12 months of sales list to see how many cases of each item code they ordered. This created around 45k rows with about 15 columns of formulas. Needless to say that does not work and absolutely destroyed the computer.

My next attempt was to add the itemcodes the customer has purchased and only those, but would require manually checking for new item codes each month, which I would prefer to avoid, but I will if this is impossible.

My request is to have the second idea done and have the ability to see if a new itemcode for that customer is pasted into the data dump section. If so it inserts under the last itemcode / customer combo and shifts cells down. Preferably it would format everything to the above information and style.

Not even entirely sure if this is possible.

The file has all identifying information deleted, but the blank columns normally have data in them. Right now only the current month and current year have the SUMIF formula since I copy and pasted the rest to values to save space. Not all of our customercodes are there.

Let me know if it is possible if not I will find a different way thanks.