This is the case when diffusion in the interior is possible (like in the liquids) or when the initial small crystals are allowed to recrystallize. Kinetic effects (like speed of crystallization and presence of mixing) play a role.
This scenario emerges when molecules can move freely within the interior (e.g., in liquids), or when tiny crystals are permitted to grow into larger ones. The rates at which crystallization occurs and the effects of mixing also come into play.