So... I just finished S;G 0 true ending and it kinda left me confused, and after thinking for a long time here's what i can make up:
1. Okabe from "Promised Rinascimento" sent a D-Rine.
2. Okabe from the past received the D-Rine and goes through "Vega and Altair" route.
3. A while after VA ending, PR Okabe experienced Reading Steiner and replaced VA Okabe.
4. Okabe goes through several more world line jumps sometime before "Milky Way Crossing".
5. WMC Okabe made a recording to help the original Okabe and used the time machine before sending it so Reading Steiner won't activate, thus preventing him from replacing Okabe in the Steins Gate world line.
Let me know i got it wrong.