Maybe it hasn't been 3 months? My head cannon thinks it's been maybe a year or so. I mean A lot of things happened since Oro died, both times.
But Yeah I'm still confused about the unbound arms thing. Maybe it was information Kabuto received from Obito during their tenuous partnership. Like the mask and its location. But I guess that opens a bigger can of worms... why wouldn't Obito want to release the souls of the 4 hokage to fight on his side? The only thing I can think of is maybe these souls aren't bound by the edo tensei and are just going to be info dumps for Sasuke/the reader. Or maybe Obito feared the first and second may of unbound themselves from the edo tensei like Madara did. They were of comparable skills. and If I remember correctly the second was a master of edo tensei.