Your vintage baking powder and your mid cakes are almost certainly the same story. Expired leavening is the #1 SILENT cake failure - it doesn't smell, doesn't look different, just quietly stops lifting, and the baker blames the recipe, the oven and themselves in that order.
Raising agents degrade in India's humidity well BEFORE their printed dates. The rules: buy small packs, store airtight, replace within about 6 months of opening. And test the suspects - baking soda should fizz enthusiastically in curd; powder should froth in hot water. No fizz, no bake, no mercy.
The others age less silently but still matter: old butter carries off-flavours into everything it touches, old eggs whip poorly and announce themselves. And a quieter business point - products made with borderline ingredients also AGE faster after sale, silently shortening whatever shelf-life you promised the customer.
Retire the vintage, date your packets when you open them, and watch the mid-cake era end 🙂
