If you execute addWeaponGlobal on the server several times the receiving unit will get the weapon added several times too, although visually it looks like unit has only 1 weapon. But opening inventroy and dragging the weapon to the ground reveals many copies.

Also:

If unit doesn't have any weapon, adding a weapon with addWeaponGlobal will not make unit automatically select it.

After adding multiple copies via repeated addWeaponGlobal command, while unit has already the weapon selected, dragging weapon to the ground will make unit to deselect it, yet there will still be copies in weapon slot.