Hi Frank,
All patches are grouped in properties(lists of patches) according to their compliance status. You can see these properties by running:
$complianceStatus | gm -MemberType property *patches
I suppose that the patches you are looking for are not with NotCompliant status, therefore the $complianceStatus.NotCompliantPatches list is empty. They should be represented in some of the other properties (patch lists). Could you check this?
One more thing, I presume that the $complianceStatus in your case is a single object. If it is an array you have to explore each element of the array. Each element represents an association between
inventory item - baseline - patches included in the baseline, devided by their status.
Thanks,
Biliana