Google has decided to sync to mobile devices only contacts that are labeled with “May Contacts“. Thus, it’s most likely to forget about the extra label and then the important new contact will not be synched to the mobile device (You will for sure notice it once you realy need the data when on the road).
eM Client could be helpfull here with an automic (option) to maintain any new contact with the default category „My Contacts“ even though it has not initially been created in the „My Contacts“ subfolder.
That would help to prevent from missing contact data on the road.