'벌써 추운 겨울이 가고 따뜻한 봄이 왔습니다' and '벌써 추운 겨울이 갔고 따뜻한 봄이 벌써 추운 겨울이 가고 따뜻한 봄이 왔습니다' In an example the first sentence was givem.. However when 오다 is in past form shouldn't we be using the past form of 가다?
In English, in a phrase like "winter ended and spring started," tense must apply to both verbs. However, in Korean, tense is required only for the last verb: for the preceding verb(s), tense is optional, and it is much more natural to just use the present form unless you have to emphasize the tense.
겨울이 가고 봄이 왔습니다 : OK
겨울이 갔고 봄이 왔습니다 : less natural (duplicated past tense marker)
겨울이 갔고 봄이 올 것입니다 : OK (they belong to different times, so you want tense in both verbs)