Domains are curated. MY LISTS gathers anything you import that doesn't match a curated domain — each keeps its own progress. Bold means you've made progress in that domain.
One rule for your own lists: within a domain, every entry needs its own ID — never restart numbering in a new file. Progress is tracked per ID, so two files that both start at 0001 would share scores between different words. WordDock checks this when you import and warns you.