hi haldi
we have to remember that it is not just the aforementioned that are fried in the oil but a countless number of other ingredients are too peppers/onions/garlic/mushrooms/aubergines/samosas(lamb and vegetable)/pakoras(chicken and vegetable) onion bhajis twice! and it all will be recycled back into the curry gravy or if they use the fryer to cook them them that oil will be re-used in the curry gravy complex oil to say the least. dependant on the pre-cooking methods ie bruce edwards methods of cooking the chicken/potatoes/cauliflower/tarkas(onions/garlic/tomato puree etc.) again recycled! and not forgetting popadums/puris(purees) ghees butter and vegetable, just about everything that is fried excess will be in the curry gravy oil.
anyway haldi you are not in the minority thinking that the recycled oil is the key ingredient to obtain that restaurant smell and flavour. i have been recycling my oil and when it gets low i top up with new oil but the recycling keeps going adding the next batch of curry oil from new sauce but it does make a difference. haven't got to my local for ages now cheaper to cook my own but i do want to get some oil just to confirm that it is that and i am doing it right as you are. have just finished making a new batch of curry gravy 10 onions worth about 5 and a half litres and reclaimed the oil having used fresh oil to start with 500ml have reclaimed 300ml of red oil. the remainder is floating on top of the gravy and is a very dark red! i did add 1 dsp kashmiri chilli powder after blending( having already reclaimed the curry oil) and the only spices added to the gravy are rajver masala ( recipe posted)and turmeric (3tbsps and 1 heaped tbsp respectively). the gravy will naturally thicken as it cools and when i cook the final dish i add the gravy to a small pan to bring to boil with added water so is runny works every time.
hope this confuses matters further

regards
gary