Well that ruled out my next pick of Pedro Carrasco then! The only thing I've got to equal Gavilan is Johnny Dundee, another with 143.
I believe, that Dundee actually didn't lose inside the distance in his first 156 fights - which now is the number to beat.
I think, maybe you didn't count the fights labeled "ND"? There are 13 of those before he lost to Jackson - which brings his total to 156.
Not a bad guess! Welsh went unstopped in 161 fights - before losing inside the distance to Benny Leonard (for the first and only time in his career). 161 is now the number to beat!