One definition of staging :
T1 : Can't be felt on DRE or seen by imaging
T1a and T1b relate to tissue removed to treat BPH
T1c : Identified by needle biopsy for any reason, for example for elevated PSA
T2 : Palpable or visible tumor, confined within the prostate.
As you know T2a, b or c relates to lobe(s) involved.