After Susan brings the newspaper to show Emily her published poem, she (sarcastically) wishes Emily a Happy Valentine's Day as she exits. In the next shot, a tree with full foliage can be seen out the window. There are definitely no leaves on the trees in Amherst, Massachusetts in mid-February.
The letter from Susan handed to Emily shows a letter with a postmark but no postage stamp.
Historical inaccuracies and anachronisms abound throughout the film in the costumes, sets, and props, but it is not intended to be a faithful period piece. One notably accurate detail is Emily's unshaven legs in the next-to-last scene.