Is this really desirable though?

Knowing that different rejects came from different changesets is useful, though obviously the way arch implements currently can be hard to use.

Hmmm, since patch files can contain arbitrary text interspersed with the diffs, how about making tla somehow append to .rej files, e.g.:

   Rejects from foo@bar--baz/ack--barf--0--patch-9:
   <diff 1>

   Rejects from foo@bar--baz/ack--barf--0--patch-10:
   <diff 2>

   etc.

Since it's `patch' that makes the .rej files (I think!) it would be quite as simple as that, but tla could -- maybe in addition to moving all .orig/.rej files into a separate directory -- append old .rej files onto the end of a similarly named .old-rejs file, with a format like the above.

Food for thought anyway...

I do find the current system a bit problematic, as I tend to not notice the +...old-rejs... directories that tla creates until much later.