You opened quite a can, Dan.
Let's see if we can chop it down to manageable portions.
is this an average that every variety ranges? or does the ph differ slightly from one variety to another?
All it is is a range. All tomatoes will fit within that range, but even specimens of the same variety may vary within the range, based on growing or handling conditions. But consider that range: 4 tenths of a pH number. Less that a 14th more acid separating the higher from the lower number.
I have read that canned tomatoes have a lower ph than their fresh counterparts.
I don't know one way or the other, but my gut tells me the idea of canned tomatoes being less acidic to be faulty. I mean what is there about the processing that would remove or neutralize the acid?
That aside, if the pH were lower then it would mean the contents were more acidic. I'm pretty sure that's not what you meant to say.
Is there an @ home method that would be acceptable?
Not that I'm aware of. Litmus paper doesn't work with tomatoes because it's difficult to judge the color shifts. There are relatively inexpensive pH meters. But not inexpensive enough that you could cost-justify them on a one- or two-use basis.
Even if they were proven to be one of the accepted cultivars (is that right)
Technically, yes. But in the common parlance, "cultivar" is used for ornamentals, and "variety" is used for vegetables. Don't ask, cuz I don't know why. But, hey, I don't make the rules.
I have done a side by side test of canned tomatoes which included a couple different brands of DOP San Marzano tomatoes with two domestic brands. No two of the canned San Marzano tomatoes tasted identical to one another.
Which leads to the only meaningful questions re: San Marzanos and your mouth:
1. Did you particularly like any of those brands? And, if so, did you like them better than a comparable domestic brand?
2. Assumeing one of the brands was prefereable, is it consistent. Does every can taste like all the others?
3. Is the flavor of the one you like worth any cost difference.
Obviously, #3 doesn't apply in this case. Just as obvious, it doesn't matter what it says on the can. What you're doing is trying to find the canned tomato you like best. If it happens to say San Marzano, ok. And if it says Hunts, or Heinze, or even Safeway's Best, that's ok too.
I still don't think it would be unwise to try a different brand or method of packaging if a person has a sensitivity to something.
Well sure, so long as the sensitivity isn't life threatening.
All I was suggesting was that whatever the OP is reacting to, it's not the acid. The way she describes it, tomatoes are the only thing that upsets her system. Which means she's eating things that are a lot more acidic, such as lemon juice (and possibly even apples, but I haven't checked on that one). And, unless she's reacting to skin pigmentation, changing to a yellow tomato won't solve her problem.