One easy test if you have digital calipers, is to measure the wire diameter of the front and rear springs.
In addition to the four standard ride height rear springs that I posted above, there are another six listed on the "vw online parts catalogue".
1
3Q0511115M
coil spring
Model data: PR-1JA+0YE
1
3Q0511115N
coil spring
Model data: PR-1JA+0YF
1
3Q0511115P
coil spring
Model data: PR-1JA+0YG
1
3Q0511115Q
coil spring
Model data: PR-1JA+0YH
1
3Q0511115R
coil spring
Model data: PR-1JA+0YJ
1
3Q0511115BC
coil spring
Model data: PR-1JA+0YK
The last three aren't listed on autodoc. This isn't unusual as aftermarket springs aren't available to match all OEM part numbers.
However, the three standard ride height rear springs from the list above do have their specifications listed on autodoc, as detailed below.
3Q0511115M (Diameter 12.50mm, Length 366mm)
https://www.autodoc.co.uk/spares-search?keyword=3Q0511115M&supplier[0]=85
3Q0511115N (Diameter 13.25mm, Length 361mm)
https://www.autodoc.co.uk/car-parts/oem/3q0511115n?search=OEN+3Q0511115N&supplier[0]=85&supplier[1]=1
3Q0511115P (Diameter 13.50mm, Length 361mm)
https://www.autodoc.co.uk/car-parts/oem/3q0511115p?search=OEN 3Q0511115P
It looks like 3Q0511115Q, 3Q0511115R, and 3Q0511115BC are incrementally stiffer than 3Q0511115P as you can see from decoding 0YG, 0YH, 0YJ, 0YK
Decoding 0YG, 0YH, 0YJ, 0YK Build Codes
0YG = Weight range 7
0YH = Weight range 8
0YJ = Weight range 9
0YK = Weight range 10
You might have trouble finding the OEM part numbers from the coloured dots, as the "vw online parts catalogue" doesn't appear to list the above rear springs against the coloured dots.
In addition to the front and rear springs, you might want to look to see if there are different thicknesses of anti-roll bars. However, if you have 13.5mm diameter rear springs you might already have the thicked anti-roll bars. But I'm just guessing about this as I haven't done any research on anti-roll bars for the Passat.