In this case You have 2 options
1 check it in tables with changes CDHDR and CDPOS but they are very very big
2 check the behavior of field KONV-KHERK and KONV-KMPRS
Normally it is A and blank if there was no manual manipulation of pricing condition.
But pls have a look how it will be if price was change on order level and then this manual price is going to the invoice.