Yeah, the thing is, if Hagoromo existed in this DxD verse, along with Yasaka, the fact that they are both Nine- Tails as well. Well I don't think it would be something that Issei's budding intel reports have missed, or either of the factions. Something like a Kyoto yokai Civil war would be visible to even the History compilation committee.
My point is, if Hagoromo existed here, There would be signs. The Factions would know. Either there's going to be records of her or her influence, or Kyoto is going to have a commentable reputation in story that pertains to her, etc. At her power level, she can't just appear as next week's villain to Issei straight out of the blue. If she does, then it shows a severe failing in the factions' Intelligence divisions and significantly ups her threat level.
Even in Dxd Canon, Ophis' Khaos Brigade was able to stay under the radar for quite a while, as an organization. Yet still everybody knows that Ophis exists. Hagoromo may very well have an unknown faction, I grant you that. But someone must at least know that there is a Hagoromo that is or once was a threat and briefed Issei on it when he first started asking the general situation of the factions.
