Lacking an impediment may certainly cast doubt on the genuineness of your relationship, but I have yet to find any wording in the act or regulations requiring an "impediment (beyond your control)". If you know of any, I'd really like to hear about it.
I suppose I wasn't very clear in what I was trying to say. Sorry about that. You do have to be in a qualifying relationship at the three points in time that you mentioned. What I meant was that if you weren't in a qualifying relationship at the time of the application, entering into one afterwards will not make your application valid. I have read countless appeals cases where the one year leading up to the application date was examined thoroughly. The only way that following events can help with the status at the application date is that if there was some doubt, succeeding events may help to clarify the status as it was at that date. For example, if you were in a conjugal relationship for only 9 months at the time of application, it wouldn't help that it had become one year by the time the application was processed. It still wouldn't qualify.
My partner could not come to Canada for 6 months and extend for another 6 months. I wish it was that easy. When he came to visit me in February, he was unemployed and could only give his parent's address (where he "lived" for only one day before the trip) as a permanent address. The IO at the border very reluctantly gave him a 3-month VR, based on the fact that we had a partially complete PR application in hand (though we had no fee receipt). He asked for 6 months, but she would only give him three. Without some evidence that we were about to file an application, he probably would have been refused entry. He did get a 6-month extension at the end of the initial period, but they asked for an immigration medical to be done within 3 months of that, since we still hadn't filed the PR application. (It is taking much longer than we expected to prepare everything.) If we haven't filed by the time the extension expires, I don't think he'll get another extension.
If he could just stay here for a year, I'd happily file a common law application, but I don't think there's any way he can without us filing a conjugal one first. I've already been told sternly at the U.S. border that I "can't live in the U.S.," so I don't see myself moving there for a year either. As far as I'm concerned, I have an impediment beyond my control. He can't do a safe-sex sponsorship of me in the U.S. either.