oh i see...yes' i've created a saved search that looks at both Item Fulfillment and Invoice, then uses the "Applied to Transaction" join to combine the 2 together by Sales Order and SO Line.
It's not perfect because there are a lot of variables. For example if the IF date is 8/31/23 and the invoice date is 9/2/23 then your month to month comparison will be off.
Also if you have Lot Numbers or Partial Fulfillments it can skew the data as well