If you are using e.g. a T-shirt in the twilight in combination with the auto exposure function for flats, the resulting exposure time will vary naturally between sessions.
How about the capture module would offer the option to read the capture settings from an existing file? If one uses the auto exposure for flats you could read out at any time later what is needed for darks that correspond to a flat.
When using fixed exposure times and a dark library like I do, this could be used the other way round to create flats in line with existing darks.
There might be other use cases, when you perhaps want to add more exposures of the same target after a while. A sample from the previous series could serve as a reference to recall the exposure parameters - reducing the risk to set a parameter wrong accidently.
Just a thought to keep such a potential extension simple to follow and flexible beyond the single use case of flats->flat darks.