Of course, one is relying on good faith of those along the supply line, much like olive oil and meat, and no shady brokers are involved .

You will see "San Marzano style" as a descriptor by imitators, much as you see "method champenois" for sparkling wines that are not Champagne, or "Serrano style".for ham that isn't authentic Serrano.

I was looking in a upper-scale supermarket the other day and came across this brand, which was comparable in cost to the DOP stuff from WM. It also carried another DOP brand that was nerly 2x as much as this, or 4x as much as a can of generic tomatoes.

FWIW, ATK is the name of the show broadcast on PBS, and Cook's Illustrated is the name of one of the magazines ATK publishes (the more-simple home-style one is Cook's Country).

Cooks Illustrated also has a website. I have been watching the show for years...sometimes it gets a bit too anal about things for me but lots of good advice and I have learned a lot about food and cooking. I love the science behind things. Alton Brown is good for that too.
I think you answered your own question about major discernable differences when there are lots of other flavors involved. That being said, for some dishes I believe in buying the best possible ingredients that are affordable(at least to me---I buy a lot of generic stuff too) within reason especially when they are the major components of a dish. One good thing about buying whole peeled tomatoes as opposed to diced is that whole canned tomatoes are packed when they are ate their ripest while chopped often has a mix of ripe & not so ripe so you might not get the best flavor.

I'm hoping the Italians don't gas their tomatoes with ethylene to get them to turn colour (hope that isn't permitted under San Marzano DOP, or better yet, Italian or preferably E.U. laws). The hard, tasteless but red and perfect tomatoes one gets in N. American supermarkets may be a result of ethylene gassing , or breeding, or both.

Agreed on “style” plus as a brand name ... of tomatoes made in USA. Lol.

I’ll buy organic diced for making mexican rice and yes, there’s risk that it’s not safest but still not horrid.

The ethylene gassing for colour is fine (and oranges can be oranged the same way) but it just doesn't further ripen the fruit! FWIW, ethylene treatment is a permitted organic treatment in the U.S.

then it’s really good that it’s okay since people consume a lot of organic produce to balance the pesticide chemicals :-)

Before the misinformation wheel starts spinning, it should be noted that ethylene is a naturally produced gas by all ripening fruits. This is why it "works" to put unripe bananas in a paper bag for a day or two to ripen them up. The bananas themselves are producing ethylene, which is a plant hormone that promotes ripening.

Many fruits and vegetables are harvested unripe and gassed with ethylene in the supply chain to "ripen" them as they are distributed, however, as correctly noted above this not as effective as ripening on the plant naturally, because while the fruit ripens on the plant it continues to accumulate sugar and other nutrients from the green parts of the plant. This is one of many reasons that garden grown tomatoes are always better tasting than store bought...most store bought tomatoes are gassed.

I’m just here to day that I did a google search on SM tomatoes and was shocked to see a FT thread on the Google Top 5.