I recommend watching ScottH on youtube. He does tons of longevity tests on various coatings, sprays and what not. Unbiased, no sponsors, and uses "real world" testing that goes on for up to two years with monthly updates. He uses car hoods, left in his yard and get washed every couple weeks.
What is interesting about his tests, is there is some variability in products, as he has run multiple tests on the same product, starting months or even a year apart. Some products appear to experience batch to batch differences, and some have shorter life under different weather conditions...for example extreme heat, or lots of rain.
My own experience in Seattle is products tend to wear off first on the lower rockers, which experience a lot of spray from our frequent rain.
BTW, multiple tests on CQ UK 3.0 show around 2 years life. There are others that appear a bit better...a lot that run out in less than a year, regardless of manufacture claims or guarantees.