In 1976, I had the good fortune to meet Dr. Alan Lloyd, at that time the world's foremost authority on typing. Virtually anybody who learned to type in the 1950s and 1960s learned from one of his books. I asked him, "How fast is average typing anyway?" His answer was less than definitive, but pointed me in the right direction. He said, "Less than half the population of the world has the manual dexterity to wiggle their fingers at the speed of 50 words per minute or better."
"1950 references the year directly. 1950s refers to the entire decade. 1950’s is a reference to some fact or occurrence that belongs to the decade (e.g. The Twist was a 1950’s dance).
Though it may seem odd to have a number and letter next to each other without punctuation, the plural has no apostrophe."