IIRC, the Black Court is still a nation recognized. I believe Mavra actually used the Accords as leverage to force Harry to stay at Bianca's masquerade when he was trying to leave.
I don't think you do. The scene with Mavra was about old world hospitality rather than the Accords. A truce had been declared and accepted by all in attendance - but one that had nothing to do with the Accords. Otherwise Micheal wouldn't have been included in it or able to break it - he (as a "normal" human) is only considered food or property under the Accords.
The only wording we have is:
"The safety of all invited guests is assured, by word of the assembled court, of course."
- which doesn't reference the Accords but personal honour.
More:
When Mavra meets Harry by his grave she doesn't reference the Accords - nor does him. Everything about that meeting is old world hospitality in action rather than a treaty between nations. During that time the White Court is technically at war with the White Council but the Black Court? It's a non-entity. To quote Thomas:
"Well. Only two, for all practical purposes. The Black Court has fallen on hard times of late, the poor darlings."
Richard