CBTC and countdown clocks are orthogonal (although if you're doing CBTC, countdown clocks are a minor addition) - the A division has clocks, even though only the L is CBTC.
Thanks for the clarification. I knew that the L had CBTC and just assumed the A Division did as well. Turns out the A Division uses something called ATS (Automatic Train Supervision) which enables countdown clocks, but I couldn't find a whole of information on how it actually works.