Over the seven decades the NBA has existed, a lot has changed -- including even the name of the league, which originally incorporated as the Basketball Association of America (BAA). Differences in style of play, level of competition, rules and the addition of the 3-point line make it difficult for us to compare across eras for projects like ESPN's ongoing effort to pick the best NBA players of all-time using #NBArank voting.
One thing hasn't changed: the championship trophy for which all teams are competing. (OK, technically, that too has changed styles and names, but the concept is the same.