....but those who split should be strongly encouraged to put them back up on the site! Crowd-sourcing....
I disagree for several reasons -
Duplication and confusion: it would lead to a
lot of messy duplication of the same basic material within the forum, and a totally unnecessary amount of messy and potentially confusing duplication of notification posts.
Time factor and workload: I for one would not wish to deal with that same basic material twice over (or maybe half-a-dozen times over depending on however many members variously choose to split longer works). If I had originally posted a file in BMB on behalf of a contributor, and then another member took that file and independently presented a split version of it, I should then feel obliged on behalf of the original contributor to check it thoroughly to see whether or not it was still representative of the original contribution and that no further editing had been carried out. I think you can probably guess what my reaction to having to do this would be.

Furthermore, such duplication would greatly increase the workload of the already hard-working forum administrators who conscientiously check and approve every download post.
Respect for the contributor: contributors might not wish their primary files to become the subject of public debate as to how they can best be 'improved' by splitting them.

The bottom line is: files are provided on this forum through a combination of generosity and enterprise. Other members can download those files in the format that has been chosen by the primary contributor or agent. Whether or not the downloading member
then chooses to split, join or otherwise manipulate that file thereafter is entirely their own, private concern and that file should not shuttle back and forth within the forum
or outside it.
