As far as I know the caster angle is not adjustable measure the distance between the front and rear hub nuts both sides to see if there is any difference,
You could have worn top strut mounts, bottom arm mounts or crash damage. But if the Golf is lowered and the distance is the same the cast angle wouldn't of changed but the distances between front and rear would be shorter than at standard height.
Caster +1o45' +/- 30' +1o50' +/- 30' (degrees) these measurements are taken from a reference book which all garages should have and it will say that adjustment is not possible
If your Golf drives ok, doesn't scrub the tyres, stable at high speeds and the distance is the same with no sign of crash damage I wouldn't worry about it.