Pipino Cuevas was 15-6 when he beat Angel Espada for the WBA Welterweight title. He went on to make 11 successful defences.
Chris Edwards went from being an unknown fighter with a poor record to a very tough and determined British champion
Sonny Boy Jaro went from journeyman to P2P (only for one fight though...)! Tony Booth was always a journeyman but had success - at one point he had either most wins in British boxing or most British heavyweight wins.
Gilberto Keb Baas had a record of 33-20-4 when he beat Omar Romero for the WBC light flyweight belt. Sonny Boy Jaro is another great shout.
Salido and Baldomir are great mentions. I could also see K-9 Bundrage fitting the criteria, albeit to a lesser extent than the other two.
Freddie Pendleton and Vince Philips are two good fighters from the 90's who ended up as journeymen, but had a career revival, won a title and made a few defenses