It's a useful question. I suspect Darwin would affirm that the possibilities were unlimited. This meant the Darwinian framework was guided by a process less discreet, less quantized, less digital. Looking at the picture from a distance this does not seem to make much difference. A normal distribution for the analog or discreet product of variation would seem the same.
Analogy is the mixing of basic computer colors vs. colors produced by mixing of of tinted paints.
In the computer example the number of unique colours might be 64,000. With real paint pigments as the base, an infinite number of shadings are available. Some variations are prohibited. The envelope is pushable but there are limits as to how far the envelope can be pushed because by definition the possibilities are limited. What is prohibited must be somehow no longer prohibited.