AndyNZ

If you ignore the above observation and consider only the first timers, you can paint a pretty grim picture. Start with 100 at L1. ~40% pass.
Out of those 40, ~40% pass L2. This is really optimistic since the 40% passing at L2 will include retakers from previous batches - in any case, it is an assumption to finish painting the picture. So we have 16 (out of the original 100) people making it through to L3.
And then at L3, ~50% pass. So you’d have 8 people making it through. Again, this assumes there are no retakers.
Now include retakers (maybe run a Monte Carlo simulation in an Excel sheet - you can even have variables for June vs. Dec L1). My guess is you’d probably have like 4 people who make it through the first time around at each level.
Edit: Maybe S2000 can improve on these numbers with all his math wizardry.