the pedantic answer is that, from a rigorous perspective, 99.9999999999999% isn’t the same as 100% because the decimals don’t repeat forever. but a more practical answer would be that they are the same number. because of how computers (usually) round numbers, the stuff showing up after the 8th decimal place is (usually) junk that can be ignored.

an interesting example of this idea in practice has to do with the irrational number π, which nasa only approximates to 15 decimal places because that’s more than enough for most of the calculations they do (the linked page gives a better and more detailed explanation).