First-one Quota System was introduced in Sept 1948, it used a Regional/Provincial model for recruitment in Govt Jobs and accordingly;
Potential Immigrants from India 15%
Karachi had a 2% separate Quota
All Other provinces [Sindh, Balochistan, and NWFP] and the Princely States had a 17%
This was then revised on Nov 49 and now instead of using the term Potential immigrant, merit was used and new Quota was;
Punjab including Bahawalpur 23%
All other 15% [Sindh, Balochistan, and NWFP]
Under the 1956 constitution, its scope was up till March 71. That is for 15 years.
1962 's constitution reduced the term to 10 years, that was until 72. So actually extended the term by a couple of months.
71 and subsequent breakup of Pakistan changed not only the demography but also the weight age in terms of population shift.
Sindh started showing a heavy Urban/Rural divide as an ethnic divide between Sindhi majority in the rural and Non-Sindhi majority in Urban.
The new percentages according to the changed realities were then
NWFP 11.5 %
Azad Kashmir 2%
Sindh 19%, subdivided using a 60/40 formula of Urban/Rural division into 11.4 Rural and 7.6 Urban.
The actual Percentage of Urdu Speaking Hindustani Muhajir in the population of Pakistan is 7.6%, they are 19% of Sindh's Population, even then the 60/40 parity gave the advantage to them.
The First Quota System was implemented by Liaquat Ali Khan, it was for 25 years, that is up to Dec 72.
Three full provinces Sindh, Balochistan, and NWFP were given 15% Quota and Urdu Speaking Hindustani Mujahirs alone were given 20% in the name of "Merit " and 2% for Karachi alone, that makes it 22%.
Ironically, the 15% Quota of Sindh, that too normally went to Urdu Speaking Hindustani Mujahirs, due to their settlement in the cities and towns of Rural Sindh.
From 1947 to 1958, Urdu-speaking Muhajirs held much more jobs in the Government of Pakistan than their ratio of only 3.3 percent of the country's population. Christina Lamb put that figure as high as 40%. Whereas, some other researcher like Dr. Hasan Askari had put that figure close to 65% jobs in Government Services went to Urdu Speaking Hindustani Mujahir.
In 1951, of the 95 senior civil services jobs, 33 were held by the Urdu-speaking people and 40 by the Punjabis.