I found some new information:
Source: http://www.history.navy.mil/library/online/uniform_master_list.htm
Peacoat button configuration change:
Peacoat button type change:
Source: http://www.history.navy.mil/library/online/uniform_master_list.htm
Peacoat button configuration change:
A new convertible-type collar, permitting men to open the collar at the throat, is an alteration of the enlisted men's overcoat.
To insure a neat appearance, the old style overcoat may be worn open at the throat with two buttons unbuttoned, producing the same general effect as one button unbuttoned in the new style coat. Overcoats may be worn buttoned at the neck or CO's may prescribe that mode for military formations and other functions.
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Source: "Uniform Changes Listed: Peacoat Will Get New Convertible Collar." All Hands. 375 (May 1948)"
Peacoat button type change:
As a move to make the peacoat more compatible with the new service dress blue uniform, the Navy is now requiring men to change the black plastic buttons to silver oxidized buttons.
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The changeover to the silver buttons for the peacoat will be required by 1 Jul 1975.