The SQ flights book into R so this statement should be...
If you buy a AF and SQ ticket JFK-CDG-BOM / BOM-SIN-JFK the total distance flown is - 7966 + 11,962 = 19928 miles. VS credits 100% for AF flights with an A fare code and 100% for SQ flights with an R fare code, so you'll earn 100% mileage or 19928 miles. You'll also earn 200 Tier Points.