did you get the YF-21 FP?
my 21 FP hip joint very lose, I don't know is it same as your problem,
but I open the joint, apply some BLU-tack in the joint to solve this prolbem,
have a nice result~
about the sticker guide, as I know, the offical design also haven't much
detail marking, I just apply the round arrow sign and "21" at the right place,
you can follow the box's pic. to apply it.
and the other, because each kind of the sticker have their specify meaning,
so I think we can use the vf-1 for the reference.( better than nothing )