I posted in the 40k fluff board regarding this but I'll go on here again for the relevance. What I imagine Phoebus is getting at, is that the Lion is discovered in Decent of Angels and then an unspecified but likely a short amount of time passes to when we next see him in charge of his Legion, taking over from the White Scars. Without the book to hand I can't be sure, but I'm relatively certain that it indicated this is one of their first, if not their first campaign since the Lions discover, I seem to some thoughts or conversation regarding how young they still are to the crusade compared to the White Scars, again need the book.
Either way Fallen Angels then takes place fifty years after the end of Decent of Angels, and the Heresy is now in motion. In The First Heretic, the incident on Monarchia happens fifty years before the start of the Heresy, and by this point it's fairly apparent that Lorgar has been in command of his Legion and on the Great Crusade for some time now, certainly not new.
From this we can quite comfortably say that Lorgar was discovered many years, probably at least a few decades before the Lion was.
Which also puts any Primarch discovered after the Lion as being found within the last fifty years of the Great Crusade. Personally I think this was the author not really thinking about how the fifty years between the two novels would effect the founding of the other Primarchs, as some of them will have taken part in very little of the Crusade before the Heresy broke out. Think the time needs to be scaled back at bit more, but well, what can you do.
Last edited by Angel of Blood; 11-28-12 at 07:26 PM.