Hmm, yes true. Not sure why I had that in mind.
But there’s one key difference between a M1k and a T5577: if data gets miswritten on a M1k, you don’t risk losing all access to it. Nothing you could possibly do to it with an NFC reader will change its fundamental firmware, frequency or protocol. So whatever happens, a magic Chinese chip should always be able answer the magic Chinese command, and you should always be able to wipe it, read it or write it.
I did lost (regular) access to my glass M1k once when I was originally programming it as a key to my front door. Got me sweating for a minute. But it answered cwipe without any problem, and then a bunch of writes later, I was back in business.
That’s why I was a bit surprised by your stating it was possible to weird out the chip with bad coupling.