@gaelds Any news on this?
Thinking a bit more about your request I wonder about something. Where have those 700 PCs being used before? They seem to have Windows and the fog-client software installed. So my guess is they were in use maybe in a different department. Were they connected to that exactly same FOG server ever before?
I have found a bit of time to test this myself and I cannot replicate your issue as described. What I did is: Imported a single host via CSV, started the client and watched the fog.log and saw that it connected and renamed perfectly well.
So I guess Quazz is on the right track here. Please let us know what you find.