User88,
Many medical standards are local in nature. This has proven to be the case in my area for bladder cancer care.
The timing of when a urologist makes the referral to an oncologist varies. It is a call made by the individual urologist. If BCG is the ONLY cancer treatment offered by the urologist, and if BCG is suspected of not providing adequate results, that would be a time to refer to a cancer specialist - the oncologist.
A PET scan differs from a CT. The PET scan focuses on active tumor cells that show up after being marked by an injected radio-tracer. Again, it an individual doctor's decision when to have a PET scan. The urologist may want more information.
It sounds like you have an urologist who feels you deserve care outside his/her area of expertise, or the local standard of care may recommend involving an oncologist after a certain amount of time.
Adding an oncologist does not necessarily mean something is wrong. It makes sense to have a second opinion at some point in time, and to evaluate your situation using the tools that are available locally.
The nice thing about standards is that there are so many from which to choose.
Best,
Jack