PMCIDs are assigned by PubMed Central (PMC) after we submit an article's full-text XML. We routinely submit articles for all our journals indexed by PMC.
Our system automatically submits new articles to PMC within two weeks of publication. PMC then takes a few additional weeks to process the submission and assign the PMCID, after which it will appear on the article page and in PubMed.
If a PMCID is not available two months after publication, please contact us at support@jmir.org.