just because the bleach has been rinsed out twice does not mean they didn't go back and add sizing. Sizing is added back to most if not all " washed " cloth.
All I know is that white Hob Nail will come out blue white when washed in hot and strong detergent, from my experience. It arrives on the bolt a little softer shade of white, like chalk.
And, yes, it's very elastic.
Sizing is acceptable to me, it makes it easier to sew. You need only be aware for the sake of promising how washable it is. If it got lighter in spots and not entirely, it would then perhaps be a problem.