There can be less color in the result, yes. In a pixel, each color channel can take only one of 256 values (2⁸). Each adjustment transforms these 256 values to some other 256 values. But there is a constraint: for any pair of two values of input, the highest value of the two must remain the highest (otherwise you get an effect called solarization). If you use the Curves, this means that your curve cannot go downwards from left to right.
Now, consider a value somewhere in the middle, for instance 128. Your adjustment moves it to 140. The 128 values below 128 are mapped to 128 new positions between 0 and 140 (of course this means that some values below 140 won't be used. And the 128 remaining values (128 and above) are now mapped into 116 values. So you started with 256 values, and now have 128+116=244 values.
This can lead to what is called a haircomb histogram:
The histogram above is a linear black-white gradient, in which, using Curves, I moved 128 to 140. The gaps on the left are the 12 values that are left empty (128 into 140) while the teeth on the right are result values that correspond to two input values (12 of them, 128 into 116).
Each such adjustment eats a bit of color. This not too visible in the beginning because you have three color channels and the missing values don't apply to the three channels at the same time (sometimes you can even get more colors...), but in flat areas with uniform colors you will get visible bands.