I naively/accidentally purchased a fake about 10 years ago on eBay, and this was my experience with the elastic too - especially after a wash. However, as MikeDT suggests, if it is from an "unauthorised second-run production", it would be 100% identical and you'd never know.
I had a similar experience - they looked legit in the pictures but when I got em home they were obvious knock-offs. Should have known that the price was too good to be true. I ended up selling them to a 2nd hand/'vintage' clothes shop for about what I'd paid for em, so no huge loss but a lesson learned.