Health information lost from iPhone when iCloud was enabled

I'm helping a friend, who I recently helped turn on his iCloud account on his Mac computer (so he could use his iCloud Drive). To do this he needed to verify his credentials using his phone which also didn't have iCloud enabled. To verify his credentials we were required to enable iCloud on his iPhone.

Four days later he comes to me and tells me all of his Health information is gone. He now has four days of health information in his iCloud and on his phone. What happened to his previous years of data?

I am thinking that Apple has configured the software on the iPhone to store health data locally when a user doesn't' enable iCloud, but when they do enable iCloud it completely supplants that data with no option to merge and doesn't tell you it will be gone if you don't back it up first. And, what would you back it up to if you don't have iCloud enabled to begin with and enabling iCloud wipes it out?!

The reason I am posting this is to ask, "Is there any chance that the old health data is ANYWHERE?"

The other reason I am posting this is to tell people to BEWARE!