Vlookup to pull in sales data based on the month sales begins

Hello,

I have two sheets of data (spreadsheet attached). The first sheet has monthly sales data by account, but does not take into account the starting month of each account - it just knows what the sequential sales will be month on month.

The second tab shows how many accounts come on board each month.

Is there a way to use VLookup, to interrogate the first sheet for the sales data, and add it to the second sheet so that the revenue is captured for each account, commencing from the month the account becomes revenue generating? Each account becomes revenue generating in the order they are listed.

Any help would be greatly appreciated.

Many thanks!