The commonly used naming of the levels is I assume based on the plan in David Bick's book, which was based on research my parents did about 50 years ago. The level numbering was based on the highly suspect plan from the short lived working in the 1870's.
Unfortunately they did not go in any detail into the surviving plans & records from the main period of working 1880's-c1916.
The correct names should be, going up on the main lode from above Glaslyn:
Level B (shown as New No. 1 almost certainly never called that) which is the one at the aerial ropeway end.
Level A (shown as No. 1) (open)
No. 1 (shown as No 2) (blocked)
No. 3 (open) & No. 4 are below the small lake
The 1911-1913 plans just show Nos 5, 6 & & above the lake, I managed to dig into at least one level probably above these (shown on DB's plan).
For underground access permission was required from the CCW office, I assume this is still the case.