Identifying a River Cooter

Here's a River Cooter along the Delaware Raritan Canal last May. I'm going to try and explain how I arrived at this identification. Despite living in New Jersey, they're not documented in my Field Guide to Reptiles and Amphibians of New Jersey [1], so I went to the internet for some basic information. Here's what I can tell you:

• The plastron is yellow, not reddish-orange (female) or pink (male) that you would expect to see in a Northern Red-bellied Cooter. Also, Northern Red-bellied Cooters frequently have jet black heads and necks, while this turtle has noticeable yellow there.
  
• The carapace lacks the prominent lines around the scutes that you'd see in a Painted Turtle.
• It also lacks the rich tapestry of lines on the head/neck that you'd see in a Common Map Turtle.
• A Red-eared Slider normally has a prominent red blotch about where you'd expect an ear to be, and a Yellow-bellied Slider should have a prominent yellow blotch in that same spot. I also think that Pond Sliders (both Red-eared and Yellow-bellied) tend to have straighter yellow markings on the carapace, though that's not something I read as a field mark.
• Basically our cooters and sliders can look fairly similar, and after I've found disqualifying reasons for it to be a Pond Slider or a Northern Red-bellied Cooter, I'm left to surmise that this is a River Cooter.
  

May 10, 2023 at Delaware Raritan Canal
Photo 282314787, (c) jpviolette, some rights reserved (CC BY-NC)

[1] I actually had a brief email exchange with someone working for the state who indicated that this field guide covered what was believed to be the most common reptiles and amphibians in NJ but that some smaller populations (mostly invasive ones) weren't included. While I see River Cooters semi-regularly, the field guide was published in 2002; perhaps River Cooters weren't as common 25 years ago?