Yes, particularly after long term lowcarbing but doesn't stop the diet been ketogenic.
I know long term non diabetic low carbers that after a year still have ketones in their ketostixs, can't comment on the contrary case cause I haven't met or personally seen any, I doubt ketosis stops if you are running on fats, but that is as I understand it. I might be wrong.
You said you were 99% sure you were on a ketogenic diet though, we are both doing Berstein, but maybe the case is that you are not having ketones ?(assuming you have been tested at some point while dieting at your nurse or something, mine asked me for urines next time I see her) .
I would test out of curiosity if nothing else. I only test cause I was given the ketostixs in case my BGs went high after leaving the hospital, but always had known ketosis breath. I've been having purple sticks every time I tested (occasionally I admit not everyday or anything like it) including morning fasting.
Personally, I'm in ketosis though (I will trust the sticks since that is what they used when I was in hospital), following Bersteins protocol of 6-12-12, eating 7oz plus of protein a day and enough fat. The picture I just took it after coming home, less than six hours after eating, and after coming back from training.
If you find out that you don't have ketones, it would be great to know and see if that is the long term consequences of Dr. Bersteins approach?