My Personal Opinion. Changing the cambelt on a commercial Transporter averaging 10 to 20k miles per year and used virtually every day at 100k is fine.
A California also used as an everyday vehicle averaging 10k + miles per year is fine.
BUT a California as a 3rd vehicle used occasionally and unused for weeks or months at a time, different ball game. The cambelt, under tension, in one position for extended periods of time - I wouldn't wait for more than 40k miles. Maybe that's why VWUK quoted me 40k to 100k miles. Time will tell.