Ok so, the final display gamut, initial source color gamut, and working gamut are three separate spaces. Effectively, the gamut defines where your primaries are

Ok so, the final display gamut, initial source color gamut, and working gamut are three separate spaces. Effectively, the gamut defines where your primaries are, which are the positions of the unit RGB cube within a larger volume. These three working spaces can be all completely different, and the only thing to ensure is that you are consistent about transforming from one space to the next. It's possible to do operations that take you outside the final gamut, after which you clip or do some other operation. There are no hard and fast rules, although some approaches will certainly look much better depending on lighting conditions (color temperature) and so on.