“The Medicare Administrative Contractor (MAC) portal MBI look-up tool will only return an MBI if the new Medicare card has been mailed; this avoids potential confusion if the MBI is used before the beneficiary receives their new Medicare card/MBI.” Read more: https://www.cms.gov/Outreach-and-Education/Outreach/FFSProvPartProg/Provider-Partnership-Email-Archive-Items/2018-05-17-eNews.html?DLPage=1&DLEntries=10&DLSort=0&DLSortDir=descending#_Toc514225692
