William,
I checked one wheel. It appears to be K18 12. On the other side of the stem it's harder to read but it's either 11 or 17, then the YH code. I don't know if the others match or not as far as the date goes but they all have a YH stamp, I'll have to investigate that further. Only have 4, there hasn't been a spare with this car since I've had it.