@black_elk I did not know there was a version where you didn't know the result of the attacker die before choosing 1 or 2 dice. Regional releases are so confusing but this has been an eye opener. Maybe I can research more and write a paper on those as well, thx for the inspiration
If I had to choose I'd probably go with what I already played with during my childhood and use the pick your # of die while defending rules

pps. Knock on thought, cause I just looked it up and that seems to be the case -different printings of the rules in regional releases. I'm sure that's a recipe for all sorts of rules lawyering when travelling haha

It raises an interesting issue for things like tournament rules (thinking again in the A&A context) since usually the rules there have different victory conditions, like with the cap on the game round so that players have to adopt a different style of gameplay vs the clock. But then I think for the average person who just has the boardgames in their closet, they will always defer to what's written in the manual. So like even errata and faqs may be disputed when someone holds up the game manual and says "but see, it's written right there!" hehe. I wish more games like A&A and RISK would have a lengthy and stacked to the hilts appendix. Like for A&A could easily have all the setup cards as a page X in the book, or for RISK all the many variants with optional extra zones.

For me the gold standard remains RISK II by microprose, but that's only cause it was what I had growing up. That and the 1993 physical release, which has my favorite color combo!

Wasn't sure if I understood the question, cause the framing was different than what I'm used to playing.

"The defender then observes the roll of the attacker and decides whether to defend with 1 die or 2 dice."

Unless the rules have changed in more recent editions of Risk, I think this is maybe a bit off?

In Risk I've played both players must first state how many armies/dice they intend to roll, and only afterwards would they then roll those dice (simultaneously) to determine the outcome of the battle. So the situation outlined in the survey would not arise in normal play. The Defender would only know that the Attacker intends to roll 2 dice (ie attacking with 2 armies) but would not know the actual values of the attacker's dice before deciding whether to defend themselves with 1 or 2. If it is a form of asynchronous Risk, say players are playing via email and not a live game where both players are present at the same time, I believe the standard method is for the defender to just always roll 2 dice when available, so as not to delay the attackers turn with defender confirmations for each battle round. A&AO had to manage a similar issue when developing a way to play A&A asynchronously with an order of loss in the profile, but that's not the standard for most tables or tourneys, where the defender still gets to choose and the attacker must sometimes wait for the defender to respond. Or basically if the attacker is assigning the casualties for the defender, that they do so with the defender's best interest in mind (effectively playing for the opponent to save time.) Again though might not be applicable for the specific Q you're asking re: RISK.

ps. Are those the Dutch rules? I remember hearing about them before but I've never played that way. I think there is maybe a difference in how RISK has been played in Europe vs how it's played in Britain and the States which could explain my head scratching. It may skew the answers a bit, as my first thought was 'wait what?' lol

Best of luck!

@rogercooper That's what is right But do you calculate all the possible scenarios? Especially if you are rolling all attack and defense rolls separately? That would be a huge burden imo