Dan,
I stored the cuttings during the pre-chill at 38F which is far too cold for rooting. The purpose of the prechill was to test what I have read in some places that this has a benefit to rooting results. So I set up complimentary groups that were chilled not at all, for 1 week or 4 weeks. From the rooting times you can see that the longer chilling time resulted in a shorter rooting time as measured from when they were first brought out of cold storage and into the nursery (what I considered the beginning of the rooting process). So clearly, the prechill did have an effect. You can also see that for the longer chill periods, the standard deviation is less, meaning that particular group had more consistent results. Finally when you look at the hardwood results, you can see that the pre-chilled had a higher success rate. So, there was a definitely a benefit to pre-chilling - it gave a higher success rate, less variability and shorter time (from start to rooting).
I have also rooted "summer cuttings" and they were successful. This does not conflict with the experimental results.