Six clients, six lists, and each one clean. That separation is not an accident. It is how you avoid mentioning one client’s work in front of another, how you scope an invoice, and how you hand over cleanly when an engagement ends.
The price is that your actual week is spread across six places. To answer the question of what is due by Thursday you open six lists and hold the answer in your head while you do it. And the reverse question, the one that matters more, is worse: which engagement has gone quiet, and how long has it been quiet for.
Merging the lists would answer both and destroy the separation. So most people just keep opening six lists.