Well, to me, the numbers are a wee on the high side to say he needs no insulin; it looks like he may be struggling. Here's a visual for you...
Imagine going for a walk with someone who is a speed walker; they are no strollers.
You, on the other hand, are just a normal kind of walker who's in no big rush.
This other person needs to walk fast - it's just their normal speed, so you are trying to keep up and also carry on a conversation...
Well, for the first mile or so, you may be OK with it, but then, at some point, you start to feel the strain on your body and you're not doing as well with the breathing to be able to keep up the conversation, so you start to do more listening so you can TRY to still keep up.
The longer the walk goes, the more of a strain it's getting to you, and at some point, you may need to just stop and take in some big gulps of air to try and 'right' yourself again.
I think the food has helped your cat (how long ago did you switch foods and from what to what), so that you don't need to give lots of insulin, but the numbers you are getting on the LC look like your cat is struggling on his walk and maybe a bit of insulin would help him. There are some cats who have normal numbers around the 40s, like one of mine, and others have a higher normal maybe around the 80s-100s, but Thurmond's are almost all over the 120 mark, and with his eating very little, you could expect the numbers to be higher if he was eating more.
One other thing.... how's the neuropathy going? Are you giving any B12 for it?
Since Thurmand may not need to be on insulin for long, you might want to think about getting a single pen from someone or some place. Go with Lantus or Levemir and forget about the NPH.... you get what you pay for..... buy some cheap stuff and you won't be doing Thurmond any favors.
You were smart to fix the food issue first because now you can see his true numbers on low carb foods.
ETA: the food test is a good idea but if Thurmond isn't big on the food yet, it will be tough to tell from any food test. Your ss is showing his numbers are dipping around mid cycle or so, BUT he's looking like he may need a bit of a hand for a short time.