Another random stream-of-thought from Zack's EC story and Crisis Core:
A) Zack and Kunsel were good friends. They trained together before SOLDIER, entered SOLDIER together, and were shown to be good buddies. So much so that even after Zack was declared dead, Kunsel continued to email him and reach out to him, trying to help.
B) Not only did Zack not leave Cloud behind when escaping Nibelheim, but he didn't take him anywhere else, either. Zack would have known that organizations like Avalanche or towns in Wutai would have welcomed them as Shinra traitors, and there were places where Cloud could get professional care...places he would have had to leave Cloud behind at. He didn't trust anyone enough to leave Cloud with them, not with the Turks out there or worse.
C) This means that for nine months (I think that's the timeline), Zack took care of Cloud. Mako poisoning is a mind disease, not a physical one, so Cloud was physically fit. He even physically responded sometimes, often walking in the direction where Zack steered him. But he was nowhere near self-sufficient. Zack would have needed to feed him--possibly breaking his food up first so he wouldn't choke since he couldn't chew--wash him, clean him up when he undoubtedly soiled himself, track those evacuation habits to make sure there were no problems, make sure he slept, carry him when he couldn't/wouldn't walk, physically inspect him regularly to ensure there was nothing wrong, etc.
D) Zack does a lot of stuff for a lot of people, but he's not doing that for just anyone. He and Cloud were GOOD friends, they had to be. They were both stationed in Midgar for the two years that Crisis Core spanned, even if not on missions together, they'd have ample chance to hang out. This is supported by:
E) In Remake, an infantryman recognizes Cloud in the Shinra building. He says the others said Cloud "must've gotten smoked" but that he didn't believe it (which is evidence for the idea that Cloud was a very competent soldier in the army). He then tells Cloud to wait there, because he's going to get Kunsel.
F) This random infantryman who Cloud went through training with knows Cloud was missing, and knows to go get Kunsel. There is no reason to go get a SOLDIER Second Class because a missing enlisted army man shows up. Unless:
G) Because Zack and Cloud were good friends, and Zack and Kunsel were good friends, this all leads me to believe Cloud and Kunsel were at least moderately friends. Enough so that:
H) Kunsel has been actively searching for Cloud, and the grunts know it.
