Ow, that's a hard one. Iirc:
2. Story of Yanxi Palace and Princess Pearl - on Emperor Qianlong's third empress
The portrayal of Emperor Qianlong's future third empress. She's a smart and cunning woman in the SoYP, and she's a happy-go-lucky and a bit dumb (could also be a hint that she's actually the smartest since no man likes conflict?) in PP.
3. Autumn Tale/Endless Love and Like Father, Like Son - on which one is more important, blood or attachment
The portrayal of parents-children bond on the case of switched at birth children. Unlike the former parents who choose their real daughter over the daughter who's been with them for like 15 years, the latter parents choose the son that's only been 5 years being with them which proven family is not always about having the same blood or dna.
4. Dae Jang Geum is Watching and Go Ahead - on whether a woman needs a carreer or not before getting married
FL was being told by his mother that a woman should have carreer first before thinking of marriage in DJGiW (she's 29-30). In GA, MC's best friend's mother keeps telling her to quit her mediocre job and marry a man of similar background the mother choose as the blind date partner (she's 25-26?).