Unfortunately some navs never had the VIN sticker fitted.

Only way to tell is to read the coding using NavCoder.
If it is a mono unit (which I am 95% sure it is) then a recode with NavCoder will fix it.
You need my NavCoder app (from www.siegenthaler.co.nz), an ibus interface, an an OS disc. Use V32 OS, it's the latest.