They certainly have always broken if you dropped them.
There's been something of a panic over exploding pyrex dishes (or was, a few years ago, I haven't heard as much about it lately).
Pyrex is made of tempered soda lime glass (ordinary window glass, with a heat treatment to make it stronger and tougher, and change how it breaks). It's been like that for some time, since at least the mid 1990s, when Corning spun off the business. One of the properties of tempered glass is that any chip or crack will eventually cause a failure, and it's likely to be a dramatic failure. And, of course, once the pan is in 10,000 pieces, its impossible to tell whether there was existing damage or not. it's also possible they didn't the heat treating as well as it should have been done (cheaper to do it fast, takes less energy....).
Older stuff might be made of borosilicate glass (or might not: I have corning made pie plates that are soda glass based on color and density), which doesn't rely on tempering for heat resistance. Chipped borosilicate glass can still fail unexpectedly, and it's likely to do that when under stress (like putting a cold pan in a hot oven.)