Perrin's description is not the model I have argued for. My chart is labeled "The Gradual Accrual of Logia," not stages or layers (words which I consciously avoided). In fact I wrote in the paragraph immediately proceeding the chart (Recovering, p. 97):
"The first [chart] outlines the approximate dates for the accrual of the accretions in the gospel between the years 50 and 120 CE. The chart should not be read as representing three stages of 'redaction' (literary or oral) of Thomas. Such a reading would represent a complete misunderstanding of my argument. The accrual occurred mainly within the field of oral performance and was gradual."
I think that the creation of the Gospel of Thomas was a complex, organic and gradual process, and I do not want my hypothesis to be rewritten by my critics into the exact type of model I am trying to replace, and then criticized on these terms.
The method I put into place was to identify later material from earlier material, and then to offer an explanation for how and why the later material came into the Gospel. It is not an explanation that involves redactionary layering or stages or phases. It is a hypothesis that sees later material accruing within older material in order to shift the meaning and provide a new hermeneutic once the older material became a liability or required a new interpretation. This is why I use the image "rolling corpus." The three overlapping time periods that I offer for the accrual of the later material is my best estimate based on what we know about similar material and ideas in other early Christian texts which we date to these times.