Even in case they made all that money, I can't figure out how can it be attributed to Neymar's signing?
I reckon a fraction of those jerseys that can be directly attributed to the signing of Neymar. Most of the fans decide to get a jersey this calendar year, whether it's Neymar or not. When a new signing comes up, the fans automatically get a jersey number with the new player's number because the choice is available to them. It's very easy to argue that they would have bought the jersey anyway without Neymar's name on it.
Unless they prove it conclusively that the number of Neymar jerseys sold this year is over and beyond the normal trend of Barcelona jersey sales,
and prove it that every Neymar jersey sold is only because he signed for the club, not because the fans had plans to get a jersey but chose Neymar's number because the choice was available, it's bullshit. It's like saying if Barcelona didn't waste the money on Neymar, they would have made additional money on jersey sales, because they didn't have to make up the money spent on him, a bit of scouse like logic on net spend.