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I'd need to know a little more about how the elongation was measured. There was mention of some wear on a brand new chain. That makes me think that whatever tool was used, was measuring between rollers, in which case, the reported wear was not really there.
A proper measurement of elongation is done from pin centerline to pin centerline. Wipperman does this by measuring chains over their entire length.
If you look into the specifications for a #40 drive chain, you will find that only the maximum roller diameter is defined and it's .306 inch. Campy rollers are typically .305 inch. You may find other brands with .303 inch. That would incorrectly indicate some "wear" on a brand new chain. The hole in the roller can also differ in size between brands, to add even more confusion.
I did some chain wear testing on Campy 10 chains years ago and found that my chain with 6,000 miles on it had far less than .5% elongation, as properly measured over the entire chain length, but the roller and side clearance wear were extreme. The hole in the roller had increased a lot more than the OD of the roller decreased. I purposely used only this one chain on one cassette and that cassette had new-chain skip on two of the most worn sprockets when the chain was replaced. That result contradicts Jobst Brandt's contention that only a chain that has excessive elongation will cause the type of sprocket wear that creates new-chain skip. From then on, I started alternating the use of several chains on each cassette. Slightly used chains did not skip on that cassette that previously suffered from new-chain skip.
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