You can use any tyre that has the correct profile - so Dunlop Q3s/Q4s are an example of solid tyres that aren't on Triumph's list - and even tyres that don't have the correct profile. I'm running a 190/55 on the rear instead of a 180/55, because that's all that was available at the track the last time that I was there. I had to remove the rear guard, and the tip in isn't quite as fast, but, apart from that, it's fine.
Even tyres with the same rated profile can and do differ enough in their actual profile to vary significantly and overlap with other [i]rated[i/] profiles.
A flat spot on a Supercorsa after 8,300 km is normal. On a litre-bike, a Supercorsa rear can be chewed up in a single day at the track, and I wouldn't expect much more than 3-4,000 km out of them on the road - by which point running only on the centre of the tyre will have changed the profile of the tyre enough that its geometry is quite different to as it was from the factory.