They should all be the same black whichever year car you have. What does change the colour is the suns rays over time, it can fade, also the texture of the seat facings can be a slightly different in different models. Another big factor in the shade of black, is how previous owners treated the leather, type of cleaner and leather conditioner used.
I have gone from the older Sline to a facelift A3 both with leather like you and the texture is slightly different.
If you do re-dye parts of the seat, then you can but toners to lighten the black dye, do test piece first, you can always go over it later if it looks wrong. Or, if you don't have the patience to get it right there are a few leather experts out there that will get an exact match.
Some leather care tips---
I use Gliptone conditioner every 2 months to keep the leather soft and supple. Never use detergents to clean leather just a slightly damp cloth, if you get the leather too wet it will end up baggy permernantly. Never use any type of leather polish, just makes the leather hard and shiny and will eventually crack. I've seen car dealers do this to make the seats look nice and black and shiny but it's no good for the leather long term.
