Thanks, but it doesn't help because, as I said, it does not appear in Datasets. But, having just gone back in to have a look, it seems maybe someone has helped me out. The replacement, working, package which I uploaded named PackageName2 has been renamed
to PackageName (which I couldn't do myself because a mystery hidden broken upload was blocking it).
Anyway, all good for me now. Thanks for your help, my mystery benefactor! And thanks Kohina, for taking the time to reply.