I've reached the conclusion that all my TL072's and TL074's bought via AliExpress from China are fakes. Both SMD and THT versions. Most likely they are LM324 or similar. The particular problem I've had is the slew rate being waaay off specification, something like 30 times slower than specified which is easily seen in my VCO as the output square wave starts to slew into triangles at around 4 kHz.
I've heard of counterfeits and blacktopping, but this seems like something else. I'm so surprised that there is any money to make out of this. I mean, I pay very little money (€7 for 100 "TL074CDR" for instance). This for a perfectly looking cut strips of 100 of a reel:
There can't really be blacktopping and re-packaging going on for that kind of money, can there? Can the source factory itself be faking the labels?
Any insight on this? I've tried to google counterfeits and how to spot them, but it seems most sources are old and covers blacktopping and the like. This really can't be it. Factory rejects wouldn't be like this where everyone of them has a way-out-of specification slew rate, would it?