tail wind...
As far I remember, all the -800 are not certified for 15 kts...
The -800 FCOM stated YD042 - YD045, YK402, YK406: 15 knots
YC126 - YC978, YD216 - YJ953, YK701 - YL052: 10 knots.
For the -900, it seems All are certified.
Now, I do not want to know if the pilots you are talking about are flexible or not.
But, the point regarding my first post is the contradiction it seems there is between the statements in the different manuals