Hi,
I was just approved to TDIU and mine started the same as yours, with a request for increase. With a new combined rating of 80%, I too thought that they would infer IU but I was told by my VSO that they no longer infer a claim of TDIU(this is what I was told), so we had to file a separate claim for IU. We did this right away, I mean they were processing the claim for IU less the 70 days after the C&P for the org request for increase. So in my case, they just sent the request to the Dr that had just performed my C&P and he wrote his opinion, I was not required to go to another C&P. So if your last exam was really close to this new claim, they might not schedule you for another one. Good luck and I hope it works out.
AJ