I am unsure about this. I know in 3.5 D&D when your INT increases at higher levels (either due to adding stat points or by using manuals) you only gain extra skill points/level from that point on. (i.e. if you get the increase at level 8, for example, you only start to get the additional skill points for all subsequent levels, not retroactive levels).
I am sure that I read somewhere that in Pathfinder you get all of the retroactive skill points (so if your INT modifier goes up by 1 point at level 8, then you get 8 skill points to distribute).
I have not been able to find where I read this. It is possible that I read it in a forum and not actually in the rulebooks. Can someone let me know how the rules officially work in pathfinder. If they work the way I think they do, can you link where I can find this info?