I've tried to keep this as concise as possible.

Under the German Empire in WW1 and the Third Reich/Wehrmacht in WW2, how were conscriptees notified of their conscription? Would they get a letter in the mail, would uniformed recruiters come to their houses? Was there a lottery, and if so, where could I access records of the lottery?

How were records kept of WWI veterans’ service, (rank, specialization, weapon proficiency, unit assignments, etc.) in the interwar period (more particularly, following the disbanding of the Imperial German Army), if at all? Was the Wehrpass a thing in the Imperial German Army, or were those not utilized until the Wehrmacht? Further, if records were kept, what was the chance they would’ve been misplaced or destroyed?

Since the military age under the Wehrmacht was 18-45, does this mean that “older” men (for the sake of specificity, let’s say over 35 years old) were conscripted? If so, was there a higher conscription rate in this age group amongst veterans of the first world war, provided they were younger than 45?

Tying all of these questions together— also, TLDR—

Would it have been plausible for a WW1 veteran (conscripted in 1916 at age 17) to be conscripted into the Wehrmacht at age 40? Would the Wehrmacht have access to his records of service under the Imperial German Army? Would he have been conscripted because of his prior war experience and thought valuable to the war effort, or would it just be dumb luck?

Please forgive me if any of these questions are elementary—I’m not entirely sure where to even start with a lot of this stuff and have been using Wikipedia as a “guide” for lack of a better word. Any book recommendations for further research are also greatly appreciated.