The standard major historical periods that cover the whole planet are Ancient, Medieval, and Modern. The standard geographic regions that span the whole of recorded history and that are of use to bead collectors are Europe, Middle East, India, and Asia.

Beads are identified by origin and age and these standard periods and regions are the ingredients of unambiguous simple IDs. All what you have been reading here otherwise concerning these matters is just a bunch of sophistry put forth by silly amateur hobbyists.

"Islamic" or "Roman" or "Phoenician" or "Helenistic" or "Byzantine" are meaningful terms for lots of things, but not bead identification. Think about it before you fall into the quagmire of ambiguity.