There is as much evidence to support this interpretation as there is to support the idea that all of the stone rows on Exmoor are prehistoric or indeed whether most standing stones were erected in prehistoric times. I think it would be possible to add your comment to most of the pages on the Portal. This is the reason that I do not accept any of the British rows as definite - the best that is possible is plausible. The evidence to support the idea that the Nine Maidens row once extended further to the north is based on the observation that there are many other examples where long rows are built to provide a visual reveal at their upper end. This is particularly the case in Cornwall where most of the rows have this characteristic. Whilst this evidence is circumstantial much of our understanding of British archaeology is built upon this type of evidence and to dismiss it as unfounded and speculative would seem a little harsh.
Something is not right. This message is just to keep things from messing up down the road