Every event that is converted to Mazévo from EMS will include a Conversion ID and Conversion Notes field. This article explains what is included in those fields.
The Conversion ID field includes the reservation number in EMS.
Conversion Notes includes the EMS temporary contact and contact email and phone number.
EMS Reservation Temporary Contact (if there is one). EMS included a temporary contact field that allowed a user to type in any contact name they wanted. These contact names were only stored with the reservation and did not create a contact record in EMS. If you previously used EMS Lite all reservations will include a temporary contact field.
Phone number and email address for the contact on the EMS reservation. Generally the phone number and email address on the reservation will match the phone number and email on the contact associated with the reservation. In EMS phone and email can be overridden on the reservation so there is a chance that they may different. This way you have both values and can determine which one you want to keep.