[userbinator]

If you go only on the definition of a clone being "compatible interface", then there are tons of other examples of that in the electronics industry - it's more commonly known for simpler parts like voltage regulators (how many companies make a '7805?), opamps, transistors, etc. but also occurs with more complex ones too.

IC companies make unadvertised products all the time, for anyone who is willing to buy enough... look at Apple's Lightning cable and TI's BQ2025, for instance.