Ok, thanks for this update. But my confusion still remains. Let me clarify it.

In my childhood I used to travel through HWH Old Complex and I clearly remembered that the last functional platform I had seen there was PF No 15, whose length was just enough to accommodate one EMU rake. During the year 1996-97, we had traveled to Puri in Sri Jagannath Express (Number was 8409). It departed from PF No 18. That was the 1st time I visited the New Complex and at that time the New Complex had...
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only 4 PFs (18, 19, 20 and 21). There was no sign of PF No 17, also 22 and 23 there during those days.

Now I am stating where my confusion is. If the Old Complex ends in 15 and the New Complex starts from 18, where exactly PF 16 and 17 used to be at that time? Those platforms had to be somewhere, otherwise the numbering can't suddenly jump from 15 to 18. Ok, they constructed PF 17 later in the New Complex, but then where the 16 used to be at that time? Can anyone who has got a knowledge about the old PF layout at HWH, kindly clarify it. I am eager to know.