heres how to merge all at oce
make sure all verts are close to each other pref ontop
shouldnt be hard if u dup correctly


select all an chose combine
click merge verts an options
set dist to 0
in channel box chose mergeverts from that list click it an at the bottom of the list will appear some attributes u can change
tweak the dist to like 0.1 or so by typing or click text an middle mouse drag
turn on border edged to check an that should do it