Yes all of our buttons are IL and yes, some of them are their OEM version which is supplied to re-sellers (Happ?) so don't have the IL logo, but are exactly the same button.
Nobody has mentioned micro-switches yet (probably just as well as the thread will go on for ever!) but ours are Chery D42 which over the years we have received the best feedback from. IL themselves don't supply these switches with their buttons, they generally supply SAIA but we source the Cherry separately from the buttons.
I have boxes full of sample buttons from Taiwan and China. They are generally direct rip-offs of the IL buttons but the dished face is always uneven and they have a dull appearance so have not been tempted to sell these.
Andy