As long as the oil you pick claims the 504, either on bottle or website, I wouldn't bother worrying about. Labels get updated/changed constantly and spec's are added as the formula passes, gets approved, recommended, or is tested for it.
I wouldn't have used the lower HTHS Mobil1 5w30 API stuff... but your engine isn't going care about 8 ounces. Full level is better than empty. My Jetta can use a pint of just about ANY oil for topping off. So, a pint of API oil is just fine, especially since you at least picked a good full synthetic hopefully SP/GF6.
I prefer HTHS and/or additives. So, any of the 3.5+ HTHS euro/hdeo synthetic oils world be my 1st choice for topping off if the 504/507 isn't available. I am not too grade picky but VW will state both a grade and VW spec, and sometimes substitutes too. Guessing you require a "0w-30" 504. Little surprised that VW didn't switch that engine over to 508 yet, for more engine racket and even more oil consumption
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In an emergency, I'd use any higher hths synthietc 0w30/5w30/10w30 or any 0w40/5w40. I've got a quart of Amsoil 10w40 mixed into a sump of 508 0w20. It just sounds better with a little more visc. Be glad that you get to use a 3.5+ HTHS 30 grade.
I also don't care for the 10k interval that VW recommends. After an initial filter change, I change every 5k miles. I've heard of many complaining about oil consumption with their 10k interval and 508 oil. I guess that you at least know how to use a dipstick, how to use the 710 cap, and do check top off often enough, which makes you better than 98% of the other consumers out there.
And, don't be surprised if the owner's manual or underhood sticker don't match, or changes with the MPG push, or confuses the dealer, confuses VW, or gets a underhood sticker update during a dealer service, or confuses vwvortex forum members.
Quickly view PDF versions of your owners manual for VW model years 2012 and newer by entering your 17-digit Vehicle Identification Number (VIN).
www.vwserviceandparts.com