Critical reasoning question stems in OG 10 and OG 12

Yeah agree with stacey on this.....

Responding to a pm:
First of all, I would not try to deduce the format of the actual GMAT using OG 10 or 12. The questions in those books are very old. GMAT is evolving at a rapid pace and it needs to since the business environment is very dynamic. If you take GMAT today and then again 3 months later, I am sure it will be a different experience. The only thing I would take away from OG is 'which basic concepts were tested some years back?'
Finally, the basic concepts are the same. An assumption was a missing premise some years back and it still is a missing premise today. The OG questions will expose me to this basic concept. They test some of these cocnepts more often now and some of them have been filtered out since they are not useful anymore. But mind you, two question formats testing the same concept could vary immensely.
GMAC does not put a lot of thought into which questions will go into OG since they are not trying to prepare you for the test. All they are doing is giving you a feel of the kind of questions asked. Therefore, don't over analyze the OGs.

Did you do OG 10 first and then OG 12? If yes, then that could explain why you felt that OG10 questions were trickier. It was your first shot at some new questions. By the time you started with OG12, you had done many 'GMAT type' questions and hence found them easy. If that is not the case and you feel that some OG10 questions are trickier, go ahead and put them in the CR section. GMAT Club members will make sure that there is no doubt left in your mind.

"Does the actual gmat put tricky question stems for difficult questions? "

It could. There is a straight forward way of asking questions and then there is a round about way of saying the same thing (and everything in between). For higher level questions, the question stem could confuse you. But that is a crude way of making a question difficult. The best thing to do in such a case is go step by step, understand the small clauses and put them all together in your own words. Focus on what you are looking for and then go on to the options. But mostly, I think, the questions stems are pretty straight forward. The added difficulty is generally more subtle e.g. two options could feel correct or none of the options could feel correct and you would need to dig deeper to get to the answer etc.

"Or is the pool of stems resctricted to the OG 12 stems?"

There is no reason to think so. Even when the OG 12 questions were a part of actual GMAT, the question stems would not have been restricted to only those in OG 12.

"I wonder why is the change across editions, to trick the test-taker or the stems on OG 10 don't appear on the exam anymore."

I highly doubt that GMAC was trying to trick the test taker. As I said before, GMAT is evolving at a rapid pace. If you pick 100 questions from its question bank today, they will be different in their format from 100 questions that you pick from its question bank a year down the line. So I wouldn't expect the questions to be similar in the two editions. That said, the difference would be more about the way you phrase it rather than the actual concept. I wouldn't expect to see the OG 10 format on my test but then, I wouldn't expect the OG 12 format either. But whatever comes, conceptually, it would not be far from the questions in either of the editions. I would be well prepared since it is the same question after all. I just have to identify it in its various forms.