They will lose most of that barring when they molt into adult feathers. Depending on how much white they have, you may see some of that barring return w/subsequent molts. Not the thick barring you see at this age but it can be seen along the back, sides, stomach and as a "frosted" look much of the time.
Here is a pic of the barring on my Charlotte at 2-3yrs. She was a black barred, pied Scovy & carried the white head gene though it didn't begin manifesting until she had molted a second time.
Yes, the tend to lose most of the barring once they molt. I have a 2 year old hen, she is black and white pied with barring. When I first got her, she didn't look barred at all. I though she was plain black and white like the others I got with her. But when she molts, she gets her barred feathers back. She is barred right now and very pretty. It's mostly just her belly and the feathers on the tops of her wings. I haven't gotten any barred ducklings from her though. I was really hoping for some, but none of the 30+ she hatched this year had it.
Here's a recent picture of her she just finished raising a clutch of ducklings and looks really scruffy for some reason.