EMDs (Electronic Miscellaneous Documents) are effectively an e-ticket for the issuance of ancillaries.
The Gordian API will return an EMD number if Gordian fulfills the purchase of an ancillary through either a direct API connection to the airline or bridged GDS credentials. If Gordian fulfills the ancillary through another method (say on airline.com) the Gordian API will not return an EMD number for the purchase.