Maybe because the test hair wasn't growing within the detox timeframe, when released old mercury was circulating? Did you use a regular blood test detecting the mercury detox?
Yeah, the mercury would have been stored and not able to be detected in any test. When I had the detox I got a urine test and that detected the mercury. The symptoms were intense and pointed to some heavy metal but I'm glad it was confirmed. Too bad I didn't know about taking binders since surely some of the mercury was reabsorbed. I've worked to try and detox any I still had, over the years. I had two mercury fillings, now I have one so I'm still having the release of mercury vapor from that one. Even though the mercury may have been from long term storage, I also wonder what effect getting a mercury filling out incorrectly a few years prior to the detox had, as well as the thimerosol from a series of flu shots I took in the late 90's early 2000's. I also ate a lot of sushi during that time.
Ethylmercury (organic mercury )is in thimerosol, methylmercury (organic mercury )is in fish, and in coal combustion in which the inorganic mercury has been converted into methylmercury by organic matter it comes in contact with, elemental mercury (inorganic) is in silver fillings and coal combustion and industrial sources, and rocks in the Earth's crust. They're supposed to have different effects, and some are supposed to be cleared from the body easier but mercury is mercury and if you don't detox well, whether because of an illness like ME CFS which can cause a methylation block, or you have trouble detoxing for whatever reason including genetic errors, you may have a problem with it.
Regarding hair testing and organic and inorganic mercury, Andrew Cutler in a paper for the January 2017 Townsend letter entitled 'Hair Testing for Mercury and other toxic metals' said in part:
"Blood and urine tests for mercury, arsenic, antimony, and lead are often normal in poisoned people. Hair tests are hard to interpret because one poison – mercury – affects how the body transports minerals. This leads to results in hair, urine, and blood that often do not reflect the body's inventory of each element.
[...]
Acute exposure to mercury results in high blood and urine levels for some
months. Organic mercury partitions strongly into hair, inorganic and metallic
mercury do not. Even in modest exposures to fish (methyl) mercury, hair levels are much higher than those typically seen in inorganic or metallic mercury poisoning. Organic mercury also partitions strongly into red blood cells and is not excreted in urine. So in acute, recent exposure, the amounts of hair, urine, RBC, and whole blood mercury are informative. This is irrelevant in chronic toxicity where blood, urine and hair levels are low; all the organic mercury has long since converted to the inorganic form. High levels still prevail in the brain and other organs – which are not amenable to sampling and have poorly understood
kinetics."