sure. 100% means something will happen every single time in the observed set. if something does not happen every single time, then it is not 100%.

this will not happen every single time. among all possible results, there will be results where none of the monkeys start any kind of shakespeare. there will be instances where every single work they start will be just the paper full of letter "a". or something else than shakespeare. as you add monkeys (approach the infinity) the smaller such chancegets, until it gets extremely unlikely, but it is not going to be zero.

imagine you are throwing a 6 sided dice hundred times and i ask you - is it possible there will be no 6 among those one hundred throws?

anyone who passed some basic math understand it is indeed unlikely, but it is not impossible. if you keep throwing long enough, there will be cases with zero 6s in it.

probability of that happening is (5/6)^100, which is 1,2 x 10^-8, eg it will happen roughly 1,2 times in ten million cases. not likely, but not impossible.

in 1000 dice throws, the chance drops to (5/6)^1000, roughly 6,6 x 10^(-80), or 6,6 in 100 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 cases.

fun fact: the above number (1 with 80 zeros) is called One Hundred Quinvigintillion (had to google that indeed).

if you further increase the number of throws in the series, the chance of not having single 6 will be getting even smaller, but never zero.

or in other word, if you raise 5/6 to any positive number, the resulting number is always positive number.

https://www.wolframalpha.com/input?i=%285%2F6%29%5En

for further study, the relevant concept here is limit of the function

we say that limit of the above function is zero, which means it will approach the zero really close (infinitely close), but will never reach it.