Great question, for a serious music aficionado. As far as original Bakersfield Sound goes, (If I recall correctly) Merle Haggard and Jean Shepard are also early artists on Capitol with the Bakersfield Sound. Buck and Merle are the 2 most notable. There's others but not all agree. Vince Gill has released an album or two that is supposed to have that sound, a search including both terms should pull up the title.
Trying to sort this out can lead to friendly disagreement, not on the PB necessarily but simply coming to agreement on what constitutes that great Nashville-West sound, better known as the Bakersfield Sound. I'll let your ears decide.
Here's a site dedicated to the Bakersfield Sound - That Bakersfield Sound
Note: If you head towards the bottom of the page, an article written by Jeff Nickell "The Bakersfield Sound ..." is worth a read.
I asked my mom if she had seen Buck Owens live, she recalled seeing Buck and his band in the late 50s at The Hacienda (San Diego), if the date is correct this would be before he was signed to Capitol (1961...?), and had only recorded a few singles. There was The Bostonia Ballroom (El Cajon), also in San Diego, that had plenty of artists grace the stage back in the 50s & 60s. My mom was fortunate enough to see the likes of Patsy Cline, Jim Reeves, and others. Tex Ritter and Carl Perkins also played TBB... It wasn't any different I suppose with the British rock and punk scene of the 60s & 70s on your side of the pond, with many young artists performing smaller venues, before they hit it big