Let's say we only talk about the resting temperature.

I clearly remember from the time I grew up in the Former Soviet Union
that 36.6 °C was considered to be the normal underarm temperature. And
37 °C underarm temperature was considered to be a threshold for a
disease (like flu/cold/inflammation). Measurement was quit precise,
with an error of ± 0.1 °C, and 36.9 °C won't get you off from school
but 37 °C would. This "standard" was also very consistent with
observations. When I was healthy temperature was always below 37 °C.
When I got a flu -- almost for sure 37 °C or higher.

Now in US 37 °C is normally cited as a "normal" temperature.

So is this because they talk about intraoral or intraanal temperature?
Or is this a result of some kind of rounding or conversion error? Or
are there many ways to convert °C to F?