Comments from Submitter:
I did not have this extra part in two parted out sets. I don't know if it needs to be deleted or marked special somehow.
Unfortunately we have no means of marking an indiviual extra as "not always present",
so it's best to assume that the presence of any and all extras is variable
- i.e. when parting out, take special care to only add extras that came in your
copy(s) of the set.