This season takes place in 1969, but the "Hang in there, kitty" poster wasn't printed until 1972.
At the diner, Don Draper slides two dimes across the table to Sally for her to make a phone call. Payphones were still $.10 in this era and did not go up to $.20 until the late-'70s.
Peggy's secretary complains in the break room that her boyfriend sent her a dozen roses and that Peggy mistook them for hers. In every scene with the roses, there are more than 12; at least 13 and possibly as many as 16 can be counted.