In case you mutually refine several building blocks at once (as proposed in tip 5-25 (mutually refine)), you should explicitly document the origin (aka ancestor or root) of the refined building blocks.
It should be explicit for every element within a refined whitebox where it’s originating (that means, where it is refined from).
You find two examples below:
Document origin by naming convention
Document origin by graphical means
In the next diagram the origin of the refined building blocks is shown by a named rectangle around the refined blocks (for illustration purposes shown in pink color…)