In the research I've done, the 127/100 set is the most accurate, correct?
It's a dogs breakfast.
Assuming I understand your question, then yes - a 127/100 gear creates a perfect metric conversion. The inches to cm thing is exactly 1" = 2.54 cm. This, was defined as a very deliberate conversion which quite interestingly set the length of a standard inch, not a standard cm.
I digress.
127 is a prime number indivisible by any other whole (integer) number.
A 127 tooth gear is used together with another compound gear (100 in your case) to work with a given piece of equipment. Different numbers of teeth on the compound gear will allow different sets of metric threads. Some compounds use 100, some 50, and some 120. They are all generally multiples of simple numbers like 5, 2, etc.
One cannot have a fractional tooth. There is no such thing as 2.54 teeth. But one can multiply fractional amounts by integer abounts to result in a whole tooth.
The underlying principle is that
25.4 X 5 =127
20 X 5 = 100
So the 100 and 127 gears are related by a common integer factor of 5 and both of those resulting numbers are integers.
Does that help?