Default Backup and restore of wifi passwords

I know that wifi passwords and some app data are supposed to be backed up to your Google account but I'm wondering if this depends on the rom that you are using. I recently got a new Nexus 7 2013 and after signing in with the same Google account I use on my one xl all of my wifi passwords were there and app data was restored when apps were installed. However after flashing a new rom on my one xl and signing in to my account no wifi passwords are there and I believe some app data is there but I'm not 100% sure. Anyone know much about this?