I had the same complaint when I read it. A linear tract (often later obliterated by the mature mine) at the beginning, and an ovate coccon in a marginal fold at the end of larval life, probably are common to multiple Parornix spp. Oddly, however, Dietz neglected to mention the important part, i.e., the form of the mine of dubitella during the main part of larval life. Therefore, especially without a specified host plant, his description really doesn't shed any light on how to differentiate the larva of dubitella from that of any other Parornix. As to your larva's feeding in a marginal fold after leaving the mine, some larvae of P. geminatella (the species that I rear on Amelanchier in IL) do this, whereas others, upon leaving the mine, merely make the fold and spin, with no feeding within the fold. So it doesn't appear that this behavior, or lack thereof, is specifically diagnostic. Given that, all we have to go on is information about the adult, and based on that, I believe dubitella to be the best match for your moth (with the inevitable caveat, "at least among the spp. that have been described to date").