The campaign setup says this.
Use the 1756 Scenario Setup and starting conditions. Use the 1759–1762 Scenario End and Victory conditions.
The 1756 scenario setup says this.
Select 2 initial hand cards (A1–2, marked with a star).
Draw 4 additional cards from the shuffled Early War deck.
• Prussia—Select 3 initial hand cards (P1–3, marked with a star);
do not select Blackmailing Brühl. Draw 3 additional cards from
the shuffled Early War deck.
The Diplomacy charts says this.
• P1, P2, and P3 are guaranteed cards in initial
22.1 under ending neutrality says this.
Immediately draw a full hand
of Strategy cards for a Neutral Power that becomes Belligerent,
including all guaranteed (*) cards unless the Diplomacy Option
It can be confusing. But I think if all the powers choose option A for their diplomacy (either by choice or for not using the advanced rules) you end up with the hand allotment given in the 1756 scenario. Just my quick thoughts.