Merging records in Raiser's Edge does not carry the addressee/salutation values when the child record has data populated and the master record has no data in these fields.
This is resolved in 7.96 patch 13, released in September - October 2018 and applied to databases in Blackbaud Hosting Services. If your database is installed locally, download and install the latest version and patch, if applicable.
Alternate workaround: When merging records, do not delete the child or From Constituent record during the merge. Manually add the information from one record to the other then delete.