MLB integrated in 1947, which changed the level of competition, rendering old stats largely outdated. MLB expanded in 1961 (and other years), which lowered the level of competition, rendering old stats largely outdated. MLB lowered the mound in 1969, which gave hitters an advantage, rendering old stats largely outdated. The AL added the DH in 1973, completely skewering old team stats, rendering them largely outdated. Through the 80s and 90s, an influx of Latin players invaded the league, rendering old stats largely outdated. I could go on but you probably get my point by now.