Anargo Primus was not the capital of the Anargo sector after the Great Crusade. I can't remember if Anargo Primus became the capital after the Horus Heresy or the Age of Apostasy, but... what was the name of the Anargo sector before Anargo Primus became capital? And what was the name of its former capital? [The answer to the second question might be the same as the first, but maybe not]
It was following the 'fall' of Sargassos during the end days of the Age of Apostasy that Anargo became the capital and eponymous world of the sector following the actions of the then Lord Anargo, Albrecht Gaius. So, Sargassos was the 'capital subsector', but I'm not sure what Destecado is calling the capital world at that time...
[glow=Blue,2,300]"Absence of evidence is not evidence of absence."
"Archaeology: Saving the past at the expense of your future. A career in ruins from the start!"[/glow]