These same detractors were commenting about the chip floating around in the body and at the same time saying it was difficult to remove---again which is it?
They were also saying it had no covering that immobilized it when clearly it does--if they went to the site for the description.
The only "surgical" evidence and complaints they fielded was from someone that supposedly got an implantation at a bar in Spain---and the item was then later "difficult to locate" except by "complicated" xray and large wound. The story seems unlikely--probably the implant was properly done at a doctors office---and removed at a bar in Spain.
The answer to your question is a simple one... When the microchip was "implanted" it moved around in the body until it became stationary and began "bonding" to the body. By then the location is unknown without a sensor X-ray to locate the chip.
They have the pet chip which nobody wants and shows how hard it is to remove. Now they are trying for a glucose chip which has to be removed every 6 months even IF/when it gets FDA approval in 3 YEARS.