Need an explanation with this one please.
1. "BY THE TIME he returned to Rome he had won awards for bravery."
2. "BY THE AGE OF FORTY he had risen to the top of political world." (event N1 (rise) event N2 (turn forty)
3. "BY THE END OF THIS WAR 3 million men had died." (event N1 three million died event N2 war ended)
In sentence N1 Why not "by the time he HAD returned to Rome" when we have in sentence N2 "by the age of 40 he HAD risen". Why is the pattern in sentence N1 different from that in N2?
The construction in all three sentences is: By = fixed time point, past perfect.
His return to Rome in #1 is the fixed time point, N2 in the way you have labelled events..