I found that distinction before, but can’t say it’s true to my experience.
I got 2 glass items with PYREX (so the apparently good stuff) and one broke when a glass blower (and it was somebody who really knows what they were doing, 50 years in the business and I worked work with him often before) tried to modify it. He also said that something was strange, that should not have happened, if it was true PYREX stuff. Then he checked the second glass item for internal stress and showed me the result: it was bad. And the broken edges of the first item also was a little bit green, so according to the glass blower some iron oxide in there, which also shouldn’t be there.
So my experience was: PYREX with all capital letters (and saying “made in France”) did not protect me from buying stuff of lower quality.
I found that distinction before, but can’t say it’s true to my experience.
I got 2 glass items with PYREX (so the apparently good stuff) and one broke when a glass blower (and it was somebody who really knows what they were doing, 50 years in the business and I worked work with him often before) tried to modify it. He also said that something was strange, that should not have happened, if it was true PYREX stuff. Then he checked the second glass item for internal stress and showed me the result: it was bad. And the broken edges of the first item also was a little bit green, so according to the glass blower some iron oxide in there, which also shouldn’t be there.
So my experience was: PYREX with all capital letters (and saying “made in France”) did not protect me from buying stuff of lower quality.