Sets, Books, Gear and Catalogs in the reference catalog contain information for which year they were released.
Original Boxes and Instructions inherit the year of release from Sets.
Minifigs inherit a timeline depending on which Sets and Gear they came in. Parts inherit a timeline depending on which Sets, Gear and Minifigs they came in. The timeline for Parts and Minifigs is updated once a day. Since some sets may not yet be inventoried, the dates for Parts and Minifigs may not include the initial year or all years of appearance.