I'm really confused by this, I have the details of a number of L4A3 marked guns, A153 is 1962, A4492 to A5438 is 1965 and A6180 to A7082 is 1966, so the first L4A3 (Marked) guns appeared in 1962, 2 years after the A5 was approved. Yet there were no L4A3 in existence to modify to A5 spec. So why did they make A3s when they could have gone straight to A5 spec?

Perhaps I'm missing something in the serial numbers, can anyone add to the list below?

L4A2 1959 to 1960, approx. 10,000 guns
L4A4 1961 to 1962, approx. 5,000 guns (These maybe actually L4A2, but I've not personally observed an example)
L4A3 1962 to 1967, approx. 8,000 guns (No L4A2/4 produced in this time)
L4A4 1968 to 1977.