Zaino get's old and the results will diminish with age.
Had a customer of mine who bought used zaino and tried to apply Z2 after it was cream color. It was a PITA to put on and even worse to remove. When I gave him a fresh bottle of Z2 PRO he was WTF. It was super easy to apply and remove compared to the old stuff. It had to have been at least 3-4 years old.
Anyway - check the zaino web site with time limits for the full Z product line.
If in doubt just chuck it - it's not worth the hassle.