Your first paragraph makes the point that maybe the interpretation of each driver to reportable rail conditions is different; just remember that many times the next train through that same section will be running on a railhead that has been sanded by the train experiencing reportable conditions. That sanding between the wheels and railhead will alter the retardation characteristics for the next train.
I’ve been asked to do controlled brake stops due to the previous train experiencing low adhesion, I’ve braked as specified in the rule book and each time I’ve stoped ok which I’ve reported back. I didn’t brake more cautiously than I would have for normally for that station stop and the time of year. Slippery rail can clear up as quick as it starts. Ask any driver whose immediately following the RHTT how terrifying that can be trying to stop normally.
Indeed it does - there's a lot of factors at play as to how and why a train just a few minutes later might have a different experience entirely. Obviously the signaller should treat the report as genuine and therefore further trains will need to test the site but as you say, the actual initial report may prevent any further problems. The same is also true - sometimes to a more extreme degree - with icy rails. Circumstances can combine together to cause significant problems and indeed this was a major factor that caused the start of the Lewisham incident in 2018.