Yo! I know that this will be most likely denied or deleted, however in my opinion Mew, Celebi, Jirachi should be recatchable at least once. Why? Most of us were seriously unlucky including myself, like sync/ivs failed and ruined all the hard work. So I have an idea! What if we can release Mew for example and it would count as not catching it in the first place (We have to battle w/ Nikola, legendary quest etc). I suggest putting a 6 months cooldown after you get your second legendary pokemon, and legendaries could be recatchable for three times in total if not twice.