It’s not a stockpile, but several manufacturers outside Europe that could fill the gap, and allow the EU to fulfill its promise of 1M shells by March. I’m guessing Turkey, Pakistan, maybe Egypt. I think it was France who demanded 100% of the shells came from EU. Having failed, Czechia is pushing to bend that policy.
“I think it was France who demanded 100% of the shells came from EU”
I believe that is correct.
The rationale given, was that it was important for Europe to develop their Defense industrial capacity. That objective has significantly been addressed, by how their program was structured, and the contracts that were awarded.
The thing that has changed, is the (short term?) drying up of the expected American contribution, which is a gap that needs to be filled.