I think there's a mistake about Peggy Carter biography in this wiki.
It says 'Agent Carter' (one-shot) happens after 'Agent Carter' (TV series).
But in season 2, it's obvious 1948, and in one-shot, it's 1946.
Here's the information on Wikipedia, it's more reasonable:
"One year later, Carter faces sexism from her boss, Agent John Flynn, who treats her condescendingly and keeps her compiling data and code breaking while assigning field cases to the male agents. The SSR's main concern is the mysterious Zodiac, which they have been unable to recover for some time.
One night alone in the office while the men are out together, Carter answers the case line to hear of the location of the Zodiac. Though three to five agents are recommended, Carter decides to go to the location herself. Fighting off multiple guards, Carter is able to retrieve the Zodiac, a mysterious serum, herself. The next day, Flynn reprimands her for not going through the proper procedures to complete the mission, and dismisses the indignant Carter as just an "old flame" of Captain America's who was given her current job out of pity for her bereavement. However, before he can officially punish her, the case line rings again, this time with Howard Stark on the other end, who informs Flynn that Carter will co-head the newly created S.H.I.E.L.D.
Later in 1946, Carter has to balance the routine office work she does for the SSR in New York City with secretly assisting Howard Stark, who finds himself framed for supplying deadly weapons to enemies of the United States. Carter is assisted by Stark's butler, Edwin Jarvis, to find those responsible and dispose of the weapons."