I seem to recall the “threaded hub pendant” first appearing around 2005. I still haven’t dug out my code library
The change came about after a prominent inspector made it a priority — even a holy cause — after his successful campaign to ban drywall screws. In the course of traveling to conduct seminars, he found many DIY extension cords with four-square boxes that had suffered from abuse. Hence the code change.
At that time I posted a picture here of a simple cord cap hanging from a pendant. I believe the conversation here was lively but inconclusive — with objections centering on whether the court cap was suitable for outdoor locations.
As far as strain relief is concerned, even UL is stumped. They have two wildly different standards and even they’re not sure when to apply each. Even 2-screw NM/FMC connectors are listed (look at the box) for gripping flexible cords in some applications. Other situations seem to require both Chinese handcuffs and compression clamps.