Now I Don’t know whether this is suited for the Halo 4 forums but I was talking to my mate a couple of days ago and I did some reading about what he told me and it turns out Commander Sarah Palmer was approached in 2553 and hand picked to be the first candidate for the Spartan IV program by none other than Spartan A266 a.k.a Jun. This of course clarifies the fact he survived reach making him the only surviving member of Noble team.
I thought this was awesome given that no one knew what happened to Jun after we last saw him leaving reach escorting Catherine Halsey. Makes me wonder whether or not he will ever play a role in future halo games, would be cool if he did.
We have known this for quite some time now 
I recomend you check out the first issue of Halo initiation.
Jun’s survival has been the topic of discussion for some time in the Halo Universe forum. You should head over there some time, the members are pretty welcoming. Also, this topic should suit this discussion:
Halo: Initiation Discussion