I suspect many dynamos are damaged because owners follow handbook and other advice and attempt to balance the lamps, not realising that the advice applies only to original wattage bulbs, and not the higher wattage now usually fitted. The original handbooks give only model numbers for the lamps so few would realise the original wattage. A 1957 Austin publication 843/C gives 18 watts for the late Ruby lamps so presumably this was the original, although some trusted sources suggest more.
Curiously the stop lamp is same as tail and the dashboard lamps, 3 whole watts! And I get concerned that no one notices the large 21 watt stop lamps on my everyday 1960s car.
For the guidance of others, amongst all the available info is there a table of model, original bulbs, and wattage ratings?
For switches which include the L terminal, owners desperate to conserve electrons can adopt wiring as the RP so the side lamps extinguish.
Headlamps 618 S.V. Presumably a Lucas part number, the figures implying 6 Volts, 18 Watts
Side, Tail, Stop and Dash all B.A.S. No. 8S, which I have found listed elsewhere (1931 MG Midget instruction manual, 1928-31 Morris Minor data) as being 6 Volts, 3 Watts.
This seems to be in agreement with your information. I must admit, they all seem remarkably feeble by today's standards. Maybe in the thirties the nights were darker or people had better eyesight !
For completeness, The 1928-31 Morris Minor used a B.A.S. No. 1S headlamp bulb rated at 6 Volts, 12 Watts, and the 1931 MG Midget used a B.A.S. No. 2S bulb rated at 6 Volts, 18 Watts. I also have a listing for a 1939 Hillman Minx with Lucas Number 106 bulbs rated at a dizzying 6 Volts, 24 Watts and needing a Lucas C45NV dynamo to run them.
I confess that my own car has the dynamo set up to read 10 amps on the dashboard ammeter with the lights off (though I have never measured this current accurately) It has been doing this for at least the last 15 years so I can't say I'm unduly worried.