We have the same problem, it's probably our 3rd biggest support issue. "Where's my stuff??"
We offer only Facebook, Google, or Email. People see the email box and start typing in their email, they forget if they signed in with Facebook or Google previously.
I'm surprised it isn't the other way around. Of course, this wasn't an issue before we added email, but we got a bunch of requests from people who didn't want to sign-in with Facebook or Google.
We still have about 70% of our users who sign-in with social providers, so I'm not completely sure it was worth the headache.
It feels to me that Apple affords the benefit of Facebook, in that users do not anticipate asking "where's my stuff". But the added benefit is the perceived security and reliability of Apple.
We offer only Facebook, Google, or Email. People see the email box and start typing in their email, they forget if they signed in with Facebook or Google previously.
I'm surprised it isn't the other way around. Of course, this wasn't an issue before we added email, but we got a bunch of requests from people who didn't want to sign-in with Facebook or Google.
We still have about 70% of our users who sign-in with social providers, so I'm not completely sure it was worth the headache.