the first Ministers

The very first Ministers of the Federation of Malaya (according to Laporan Persidangan Majlis Perundangan Persekutuan, Kuala Lumpur, 18/8/1954) were:
Dato' Onn bin Jaafar - Minister of Internal Affairs;
Dr Lee Tiang Keng - Minister of Health;
Dato' EEC Thuraisingham - Minister of Education;
Dato' Nik Ahmad Kamil - Minister of Local Government, Housing and Urban Planning;
Colonel HS Lee - Minister of Transport;
Dr Ismail Abdul Rahman - Minister of Earth Resources;
Mustafa Albakri Hassan - Minister of Industrial Relations and Society;
VMN Menon - Minister of Post and Telecommunications.

An archived photo of VIPs in 1955 included Tunku Abdul Rahman, British High Commissioner Sir Donal MacGillivray and members of the Cabinet of the Federation of Malaya 1955.

People identified in the archived photo were:
(Seated)(left to right):
C.T. Thomas
Colonel H.S. Lee
Tunku Abdul Rahman (Chief Minister)
Sir Donald MacGillivray
D.C. Watherston
M.J. Hogan
Dr Ismail Dato' Abdul Rahman
(Standing)(left to right):
Dato' Abdul Razak
C. Spencer
Abdul Aziz
A.H.P. Humprey
Sulaiman Dato' Abdul Rahman
V.T. Sambathan
Sardon Jubir
Leong Yew Koh
Ong Yoke Lin
Too Joon Hing.

Questions:
1) Was there a Cabinet change in 1955?
2) Who were replaced? Who were the replacements? Who were the additions?
3) Why Dato' Onn Jaafar who was a top UMNO leader then NOT in this particular archived photo?
4) Is this particular archieved photo INCOMPLETE?

P/S: I am writing based on what I am reading. At this moment, I don't have the answers.