Although the majority of transformed D. conanti that I have seen in my area (South Mississippi) have the characteristic bright dorsal spots, I do find larger, older individuals that have a bland pattern of scattered dots or flecks, like the individual in the photo I have attached. The pattern seems somewhat similar to that of your individual. A recent, helpful paper in terms of distinguishing between conanti and auriculatus is that of Graham et al. (2010):
Graham et al. 2010. Status and possible decline of the southern dusky salamander (Desmognathus auriculatus in Georgia and Alabama, USA. Herpetological Conservation and BIology 5(3):360-373.
Graham et al. mention that conanti can have small, light flecks along their sides that could be confused with the "portholes" of auriculatus. So if everyone isn't consistent in what they are calling a porthole, using that trait could lead to misidentifications. In the paper, they say that the number of costal grooves between adpressed limbs is a good character to distinguish these two species, auriculatus having 4-6, and conanti having 3 or fewer. Also, as others here have mentioned, Graham et al. emphasize that the species likely segregate or adhere to certain habitat types, conanti being more of a ravine dweller, and auriculatus more of a mucky, swamp dweller. I managed to speak with Graham about this, and he mentioned that if the water is seep fed, the populations at that water source would more likely be conanti, at least for this part of the Coastal Plain.