Yes, when the package is installed in an environment as dev, no fixed version is used: using Package just looks into the local version of the code – including changes you make to it.
Nevertheless, you can have a package in perpetual dev state, and yet (if you are using git for version control) register or tag particular commits, so that in some projects with their own environment, you add those fixed versions in a reproducible way, as indicated. That’s possible even on the same computer.