Thanks, Ed, your report is timely—deadline for edits for the next release is next week!
The problem with the LC/PCC-PS is that the examples show subfield 'p' in field 490, but $n and $p are not valid for that field. OCLC will give an error message. The MARC21 format on both the OCLC and LC websites do not have these subfields defined. Is there a MARC21 proposal on changing that?
2.12. SERIES STATEMENT (Dec. 2015)
Simplified policy for supplements and special numbers to serials
$a Journal of ultrastructure research. $p Supplement ; $v 7