When I’ve had an upgraded flight on my itinerary, although UA prints $0 on the receipt, the underlying ticket wasn’t updated, and the partner saw an economy ticket and gave the economy baggage allowance. I suspect you’ll get the Economy allowance at BOM. You can try printing the receipt and arguing about it, or asking UA for a refund after the fact; you could also consider filing a DOT complaint against UA if they refuse to refund the baggage fee. By law, UA is required to print the luggage allowance on the receipt, so if they’re doing so incorrectly (and they often are), the DOT should know about it.