Its a 65 plate. I did a bit of reading in to it at the time and the larger 17 inch alloys and body kit push it into the higher tax band compared to the SRi trim. I think it's like a 1-2kg/km difference bit it's enough to push it into the next band.
-1.4T (100bhp) SRi 3d (2 Oct 2014 - 31 Mar 2017) - £30 road tax
-1.4T (100bhp) SRi Vx-line 3d (31 Mar 2017 - 30 May 2018) - £140 road tax
For remapping the 1.4 N/A engine.
The 1.4 N/A engine in 75bhp or 90bhp variant is the same, there are no mechanical differences. So you see a larger gain with remapping the 75bhp variant than you do with the 90bhp variant.
Someone posted that they had their 75bhp mapped to 107bhp here >
viewtopic.php?t=2834
Might be a few more examples of it being done on the Corsa E | Owners Club on Facebook too (it's a bit more active than this forum).
It's the same for the 1.4 Turbo engine. In SRi trim it's 100bhp from the factory. In white/red/black edition it's 150bhp from the factory. The only difference is the ECU mapping. So both variants remap to the same 170-180bhp. It's just you see a far larger % gain for the SRi trim as it's more restricted from the factory.