I'm not exactly sure about the law of diminishing returns like T-Bone said. I have 'heard' horror stories about some guys who have done heavy cycles and never full recovered. This isn't typical, however it appears to be 'possible'.
I've heard that some IFBB pros are permanently on TRT, of course their cycles are extremely heavy, however if jump starting the HPTA was as simple as 1,2,3 these pros wouldn't be on TRT.