Getting a broken pin out of a B8 Valve Holder.

[Terry]

try as I may, I can't pull it out.

Have you tried pushing?

Joking aside, the flat end of the tag protruded through a slit in the insulator which I think nullifies your blob of solder idea.

Find a suitable strip of flat metal - a tag removed from another valveholder will, of course, be a perfect fit - and use it to push the broken tag out from the underside.