Has there ever been a 12–1 in the La Liga?

Yes, 1 time.

The only time: February 8, 1931, Athletic Bilbao beat FC Barcelona (Athletic Bilbao 12–1 FC Barcelona).

Nearby scores

1. 13–0 Never
2. 13–1 Never
3. 13–2 Never
4. 12–0 Never
5. 12–1 1 time
6. 12–2 Never
7. 11–0 Never
8. 11–1 1 time
9. 11–2 1 time