LARYNGEAL MASK: Is written description an affirmative requirement?

In LARYNGEAL MASK CO, the CAFC reversed an invalidity for lack of written description summary judgment:

We conclude that the district court erred in granting
summary judgment that the patent was invalid for failing
the written description requirement. The Summary of
the Invention does not require that the cuff reinforcement
be connected to the backplate. Rather, it describes a
reinforcement incorporated into the distal end of the cuff.
’100 patent col.1 ll.47-63. The Summary of the Invention
further states that “[i]n a preferred aspect,” the rein-
forcement extends from the backplate. See id. at col.1
ll.64-67. We agree with LMA that one of ordinary skill in
the art could read these disclosures as providing for a cuff
reinforcement in the distal region that need not be con-
nected to the backplate. In addition, we agree with LMA
that one of ordinary skill in the art could read the Cuff
Wall Thickening Passage as disclosing a thickened cuff
portion that need not be connected to the backplate. Id.
col.8 ll.9-12. LMA has raised a genuine issue of material
fact on this issue, and therefore we reverse the court’s
grant of summary judgment and remandproceedings consistent with this opinion.

With the text "could read," one wonders whether the written
description is about possessing something or about not saying you
didn't possess something, with one of ordinary skill filling in
the blanks.