Only PID-3-patient ID (internal ID) has changed as a result of the merge. See Section 3.5.2, "Merging patient/person information," for a discussion of issues related to the implementation of merge messages.
An A34 (merge patient information-patient ID only) event is intended for merging or changing patient identifiers. It would be used to change patient identifiers on all of this patients existing accounts.
ADT ADT Message Chapter
MSH Message Header 2
EVN Event Type 3
PID Patient Identification 3
[PD1] Additional Demographics 3
MRG Merge Information 3
ACK General Acknowledgment Chapter
MSH Message Header 2
MSA Message Acknowledgment 2
[ ERR ] Error Information 2