Those Archie digests... were they reprints of the regular comics material, all-new material, or a combination of both?

Combo. Usually one new lead story and then pad it out with reprints.

At one time in the past, they were reprints of comic material. Many different eras would be represented in one volume.

At some point when comics were no longer sold off the spinner rack at news outlets, Archie went exclusively digest. The digests would then contain new material and some reprint material.

Archie never went direct sale. When places stopped selling comic books, they moved to wherever Reader's Digest and TV Guides were displayed.