Failed to transfer imessages to new phone

Backed up iphone 6 to PC in preparation for iphone 7. Process went smoothly, new phone installed with my data no problems. But before wiping my 6 I checked that some very precious imessages had been transferred and they hadn't. A lot of older messages weren't there and weren't searchable.

Since I've been using my 7 I'm reluctant to wipe it and redo the process as I'd lose the data I've made meanwhile.

Any suggestions other than doing it over?

TIA