Thanks @Deva_Rishi. Unfortunately the older versions of the esp8266 chips have a metal covering so the 8 pin IC is not visible:
The official V3 version does away with that though so it is visible:
I've contacted the supplier and will see if I can get to the bottom of it. I've also just accepted that when it comes to these parts it's better not to be a cheapskate and have ordered some official Lolin parts... They may be 60% more expensive but they're still only about $7 NZD each (bought with NZ they'd be $20-30 ea!)