Not read the whole thread, so don't know if someone brought up the following view: those custom gauges that people said, they can measure some wear even on a brand new chain and from that they concluded that those gauges are not all that exact and that you can either file your own (guided by your new chain) or do the measuring by tape, metal ruler... Well, isn't that assuming that new chains are all manufactured to perfection?
The chains are made to some tolerance and the exact length can even vary from batch to batch. If one is really picky, maybe shop for new chain in LBS where they unwrap chains for you and you can pick the one that best qualifies as 'realy new', that is un-stretched, by your gauge.