>>34838236I thought pokeballs missing meant that only a Master Ball was able to catch the pokemon, so my first Master Ball was on Articuno.
I believed that receiving only one Master Ball meant being able to catch only one legendary, thus making an incentive to trade with friends. I chalked up the legendaries in Gen 1 along with the Eeveelutions, fossils, starters, Hitmons as pokemon you had a choice of getting, but had to trade to get all of them.