RE: "It will not stack to be Block 20. "That's too bad. On Page 11, at the bottom of Playing Order Cards, it says "A creature can have more than one card attached to it, including multiple copies of the same card. Their effects are cumulative."I would think that having two defenders next to you would be just like having two cards attached to the creature, thus stacking their effects.
I think perhaps a rephrase would be ideal in this particular situation; something like:"Block 10 - Prevent the first 10 damage that would be dealt to this creature by a source."I think this would relieve some of the ambiguity, the theory being that people would more easily understand that you can't prevent the "first" damage twice.
..."window.parent.tinyMCE.get('post_content').onLoad.dispatch();" contenteditable="true" />I get that. However since it's easier to clarify, add or rewrite a rule (possibly in a version 2.0 rulebook to be released with later boxes or downloadable as a PDF) than it is to alter card texts I think Chris' method is the better one. Also, "Named powers don't stack" covers more than just Blocking, but also Flanking like in Chris' example.