Still, I was pretty sure that similar tomatoes were out there.
I am a layman on this subject but I'm pretty sure that you are right and pretty sure that my Grandmother Pearl's tomatoes are Porters

.
Dad's youngest brother gave me the seed about 30 years ago. He said that their mother had them through the Great Depression and called them, "the Peddler's Tomato."
Okay, they aren't my favorite tomato but I've grown them every year, DW likes them (very mild flavor). After the first few years, I ran onto a description of Porters and ordered some seed. The first year that I grew them side-by-side, the only thing that seemed different was, maybe, the foliage. The second year, I gave up on that notion and decided that they were the same.
Funny thing, I asked my uncle if he would like to see some pictures and try the two in his garden. He said, "NO!" You can imagine that he had an emotional reason for that

. I think many gardeners and heirloom enthusiasts have emotions involved in their efforts. More Power to Them

!
Why would Grandma Pearl have Porters? Or, more to the question, why would the Peddler have Porters? Heck's Fire, Grandma Pearl lived within 300 miles of the Porter Seed Company (founded in 1912) during the early years of the 20th Century. When they moved to New Mexico, just before the Depression, she was within a stone's throw of the Texas border. Would it be surprising if the peddler was selling Texas seed?
I don't know if I "perfected" the plants that I have grown for several decades. For one thing, I grow only a very few of them each year. How much of a selection for quality can I make?
Once, I declined to save seed from some of that year's plants and threw out the seed that I had used. I could do that because I save multiple years' seed for Grandma Pearls and I just shifted back to older seed for the next year's plants. THAT is about the best that I could do.
Steve