I get 2-3 yrs out of micron extra in Puget sound, as did the previous owner.
Now with that in mind, I will sorta echo what mainesail is saying in that i have a pretty good build up of paint on the bottom after 25 yrs, and it is looking close to needing a complete grind down to gelcoat.
Generally speaking tho, one can paint over an ablative with a different type or brand ablative paint. There are some exceptions, look at the manufactures suggestions as to whether you can or can not paint over what you have with out doing more.
I do get some slime with my bottom, and also as mainsail mentions, it takes 5-6 knots before things seem to get removed. I was out friday, hit 5-6 knots for the first time since Oct for any length of time, and the bottom was a bit cleaner on the return than the previous trips out where we were barely over 4 knots. I'm toying with a hard paint, as we can in-water clean hard paints here in Puget Sound, but ablatives it is illegal to majorly frowned upon.
She drives me boat,
I drives me dinghy!