no NOK on dualvars, but !!1 is a NOK with 5.8.
fix AMG stringification with 5.6
also workaround missing get_sv/get_cv

but there are still upstream problems:

5.6 is broken, converts $num (IV+PV) to pure NV

5.6 and >5.10 is also arguably broken:
converts $num (IV+PV) to pure NOK+POK, not IOK+POK.