iPhone Some iMessages missing on new iPhone... How to merge?

[Turnpike]

I got a new iPhone, and I got a few texts (that for legal reasons I want to keep in order) that some how aren't in iCloud... they are on one phone, but came in around the time I was updating from one phone to the other.... now my icloud text history is missing a few exchanges... how can I merge these messages while they are still on my old iPhone before I erase it? I've tried backing the old phone up to iCloud and then backing up the new phone to iCloud and that didn't put them in place. Any other suggestions?

Thanks in advance.