Again brought up short by being unable to like stuff.
hinted, Fahrenheit got where he did because he he provided something sufficiently accurate and generally useful in the area he worked, early enough on, for it to catch on. In much the same way that most rail gauges around the world continue to be used despite not necessarily being an ideal measure, because they matched what roads were doing before that, probably all the way back to the distance between wheels of Roman chariots, which probably come from a comfortable distance between the rumps of two horses.
Celsius, like other components of International measurement system, are based on easily repeatable conditions so they can always be confirmed by anyone who needs to ensure their experiments are accurate. 0C is the temperature at which pure water freezes at one atmosphere, and 100C is the temperature at which pure water boils at one atmosphere. Anyone intersted in testing can distill water with very basic methods and if they need sufficient accuracy, can go to sea level to do their tests.
Fahrenheit requires a saturated salt solution to set "0" and (since he got body temperature wrong) there is no way to confirm 100F
except by comparing to an existing thermometer. The number depend on someone else to provide you with an accurate tool to measure. As soon as one thermometer is wrong, there's no way to find out. if you think you are comparing it to one which is right, and they don't agree, then which is right and which is wrong?