Nonlifts in S12(K(8))− are old forms
The one nonlift eigenform in S12(K(8))−
must be the old form coming from the nonlift eigenform in
S12(K(4))+.
This already proves S12(K(8))− has at least one nonlift eigenform
and hence Borcherds products are not needed to help span this Fricke eigenspace.