Gnegneri
immaculately conceived
Athletic 29-30 = 0 losses over the whole season.Wrong my friend , only Bilbao did in that era...followed by Espanyol before the official formation of the league than :
Real did it in 66/67, 79/80(18 teams league in both ) 88/89 (20 teams league ) and 96/97 (22 teams league )
Real Socidad did it in 02/03 as well
Real Madrid 30-31 = 0 losses over the whole season.
Real 66-67 = 2 losses over the whole season
Real 79-80 = 3 losses over the whole season
Real 88-89 = 1 loss over the whole season
Real 96-97 = 4 losses over the whole season
Sociedad 02-03 = 6 losses over the whole season
Source: wiki