Stanford
I don´t understand the exercise and settlement bit clearly either. I was making a list of the indexes. My understanding is that American style, if you try a credit spread straddling the index as in a volatility play, when the sold lower side moves across and goes from OTM to ITM can be assigned. This jargon gets me confused. Whereas my understanding of European type options is that the assignment thing happens only at the end of the month, at expiration.
So I have NDX for the American index and the NDS for the European.
The OEX for American and the RZA, and XEO for the European.
The RUT for the American and the RLS for the European. There are a long list of indexes more than I knew existed on the CBOE site.
Anyway if I had got that Volatility Credit Spread nuances down, I looked up to see that I would trade them on the European to avoid the dangers of being assigned on the sold side as it moved 1 cent into the money. That particular strategy would only be traded on the European index version is my understanding?
I´ve asked Trading Journal couple of times to explain assignment, but guess he is very busy making bushel baskets of money?

He was going to put it on his BLOG but never did.
You are talking something entirely different with the settlement, of which I only have a vague idea and as there is nothing I can do about it, other than closing a trade early while it is active, just forget it.