Has there ever been a 12–1 in the Primera Argentina?

Yes, 1 time.

The only time: June 11, 1905, Reformer beat Barracas Athletic (Barracas Athletic 1–12 Reformer).

Nearby scores

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