Wehrmacht replacement troops prior to 1943

In the Heer, the method of fielding replacements was from the division's corresponding Ersatz-bataillon and/or feldersatz-bataillon which was a replacement battalion and field replacement battalion, correct? Well, I have noticed that most of these battalions did not exist until 1943 for the most part, so how where would troops come from if they were replacements to the divisions prior to 1943 that did not have an ersatz-battailon? For most divisions, especially in the blitzkrieg years and even during Operation Barbarossa, they don't have a subordinate unit that dealt with replacement troops. So where would they come from? Wasn't the ersatz-battailon basically the Wehrmacht's basic training, where troops went after the Reichsarbeitsdienst (RAD)? Anything advice would help, like how it would appear in a soldier's wehrpass or soldbuch.