The special 'coinbox' dial (Dial No 11, 13, 20, 23 or 24) is only needed if the coinbox is to function as originally set up. I suspect that the Museum's 'setup' (phone & A/B box on backboard) was already wired up on its backboard - hence getting working without needing access to the terminal strip in the locked A/B box.
The Irish P&T wired the A/B box up differently to the GPO - I have the original P&T diagram if necessary.
If setup as original i.e. a coin/s needed before it is possible to dial, will allow the caller to dial the recording but the A/B box will allow the caller to listen to the recording without having to press button 'A' and then press button 'B' to recover their 'call cost
- Coinboxes in the UK were not allowed to call recorded services, Speaking Clock etc. and I assume that was applicable in Ireland.
Ian