so would you say he was present during the HH or not ?
We dont know if Fabius or the Iron Warriors manages to implant him in time for the Siege of Terra. Remember, this happens in the 7 year Age of Darkness period prior to the Siege. Not a lot of time for a new Astartes to gain a lot of experience, even if they use the 1-2 year turnaround method. Appearing during the Scouring period seems more likely to me.