What is the difference between a PMID and a PMCID?
For further information about the actual policy see NIH Public Access Policy details.
For submission Methods A and B use PMC-In Process in place of the PMCID because you will not have an NIHMSID to enter.
For submission Methods C and D use the NIHMSID until the PMCID is available. The NIHMSID is assigned during the submission process.
Once you are assigned the PMCID number refer to the above box to add the PMCID.