I have an even better idea. When updating a previous dat with a newer version, clrmamepro could give the option to create an additional difference dat by comparing the old dat with the newer one.

> Since a datfile is a plain text file with no checksums or similar and freely
> editable, there is no guarantee at all that an additional 'valid_from' and/or
> 'valid_to' flag really flags new stuff correctly. Besides of that, datfile
> authors have to handle it manually/semi automatically, in other words:
> additional work for them...which I doubt they will invest.
>
>
> Roman Scherzer
>