If they're not carrying full horn genetics they can grow weak, cuticle-free horns that while horn shaped are better called scurs. Not all scurs are deformed, some just lack proper skull anchorage and cuticle. This lamb I'm raising now got only some proper genes for horns so she's got that.
Might be a breed characteristic to grow crappy horns to start with though, I don't know. They might indeed get better.