In source maps, the mapping is done between the transformed code (like minified or bundled JavaScript) and the original source code. As long as the transformations are consistent and predictable, source maps remain effective. When you replace a unique placeholder with an actual value, you're essentially making a very targeted change that shouldn't alter the overall structure or flow of the code. This means the source maps should still accurately reflect the relationship between the source code and the transformed code, except for the parts where the placeholders were replaced.