All bulbs will lose 15-25% over the year of use. Some level out after that and people use them for even longer (14k Phoenix, for example)... and some drop off even faster after a year.
In any case, my corals have never complained when I put in new bulbs without any acclimation. It is kinda fun to take a PAR reading with the 12 month old bulbs and then take a reading with the new ones. It is hard to explain why you can drop 125-200ish PAR onto some acropora when changing old-to-new MH bulbs over an acropora with no ill effects, yet raising a LED that same amount in a few minutes will cause a coral to burn.