Recovering a site after a migration lost data

Two contracts three years apart with the same client, both about forum boards that stopped working after someone else moved the server.

The objective

The first time, the boards stopped working after a server migration. The database itself was intact, which narrows the problem down to configuration, file paths and PHP version rather than the data.

The second time, three years on, they were changing hosting providers again and a previous programmer had lost data during the move and left the boards running badly. That's a harder starting point, because the question isn't what broke anymore, it's what's missing.

What I did

On the first job, I worked back from the errors to what the migration had changed, and restored the boards without touching the database.

On the second, I established what had actually made it across before doing anything else, so the recovery wasn't built on top of a partial copy.

Then I completed the move to the new provider and got the boards running correctly.

The result

Both times, the forums came back on the hosting they'd moved to.