Do apps need to be started once to receive background data

I just recently bought my first Android based phone (Samsung Galaxy A3). One thing I noticed (or maybe imagined noticing?) is that I appear to only receive notifications (like a new message in WhatsApp or a new email) if that app was previously started (and thereby listed in the "Running Apps" screen). Is that true? Would that not defeat the purpose of notifications? I tried searching for settings that would imply such a behaviour, but couldn't find any. - Restrict background data is turned **off** - WhatsApp/Gmail, etc. all have background data **enabled** - *Sync* (from the top shortcut menu) is **enabled** - Accounts/Sync settings for WhatsApp and Google Accounts are **enabled** - I have a DataUsage warning at 400MB (reached) and a limit at 500MB (not yet reached) - Network connection is set to LTE/3G/2G (automatic) and I am in 4G currently Thats about all I could think off / find... Is there more to check?