IMO - the greater challenge in finishing what are classically referred to as "pontils" (which really aren't) - is controlling heat throughout the process. Vintage marble makers didn't have access to the kind of tool used today. Managing heat in the cane throughout the process took skill and experience - and careful time management. The center of the cane is always hotter than the outside. So necking-down has a differing effect for casing glass, outer decoration (color bands etc) and the core. And the larger the diameter of the cane the more heat was stored. And of course different glass colors have somewhat different melting points.
Finishing what is referred to as the "pontil" is fraught with opportunities for imprecision. The first time I necked-down a 2" diameter cane I felt that 6 things were going wrong....heat, rotation speed, my pressure on the jacks, time....