[p3lim]

Here we go, PLAYER_LOGOUT event saving the last index to a savedvariable, two OnUpdate scripts iterating either a new index or the savedvariable, and either of them shuts down the savedvariable one.

local index = 1
 
local backup = CreateFrame'Frame'
backup:SetScript('OnUpdate', function(self)
    if(not SomeCleverVariableName) then return end
 
    if(_G['NamePlate' .. SomeCleverVariableName]) then
        self:Hide()
 
        index = SomeCleverVariableName
        SomeCleverVariableName = nil
    end
end)
 
local iterate = CreateFrame'Frame'
iterate:SetScript('OnUpdate', function()
    while(_G['NamePlate' .. index]) do
        local frame = _G['NamePlate' .. index]
        frame:HookScript('OnShow', Update)
        backup:Hide()
 
        Update(frame)
 
        index = index + 1
    end
end)
 
iterate:RegisterEvent'PLAYER_LOGOUT'
iterate:SetScript('OnEvent', function()
    SomeCleverVariableName = index + 1
end)