Egyptian Coins 1916-1919

Hello, seeing the depth of knowledge that some of the regulars have posted on various topics I have some questions to ask about the dies and minting of Egyptian coins and I hope somebody has the answers (or can recommend a good reference).
One of the types of coin that fascinates me are the modern Egyptian coinage. On the silver coins for 1916-17 I have noticed that the 2 mints involved (Bombay and Heatons) used different master dies for both the obverse and reverse (inner circle/no inner circle, fat/thin letters etc). Does anyone in the CCF have any knowledge about why this happened? I've read that John Harvey Rowntree designed all the silver coins (but can anyone confirm this for both the obverse and reverse dies).
In particular does anyone know where the master dies were engraved (London, Bombay, Heatons) and is it possible that engravers in both Bombay and England made the masters possibly from the same drawing, but one decided to modify the design.
Were the working dies made at the 2 mints or were they made in London and distributed.
I read in Roger Dewardt Lane's book (Encyclopedia Small Silver Coins) that the Heaton's 2 piastre coin of 1917 was minted in 1919. Can anyone confirm that (and why 2 years later). Did late minting occur on any other coin.
Is it possible that mules occurred from either the wrong working die being sent out or leftover dies being transferred to the other mint. Saw such a coin on the internet and it's got me puzzled
Hope someone out there has the answers. Thanks in advance