What was the first lie in the Bible?
Genesis 2:17 - But as for the tree of the knowledge of good and bad, you must not eat from it, for in the day you eat from it you will certainly die.
Well they ate it, what happened?
Genesis 3:23 - With that Jehovah God expelled him from the garden of Eʹden to cultivate the ground from which he had been taken.
Jehovah lied. They did not die in that very day. Jehovah knew they would live so he kicked them out of the garden where they lived for centuries.
Now look at what Satan said to Eve:
Genesis 3:5 - For God knows that in the very day you eat from it, your eyes will be opened and you will be like God, knowing good and bad.
Satan told the truth. Once you learn to ignore arbitrary authority you can learn what’s good and bad for yourself.
Here’s the Hebrew word מוּת - die (as translated in the passage)
Strong’s Definitions מוּת mûwth, mooth; a primitive root; to die (literally or figuratively); causatively, to kill:—× at all, × crying, (be) dead (body, man, one), (put to, worthy of) death, destroy(-er), (cause to, be like to, must) die, kill, necro(-mancer), × must needs, slay, × surely, × very suddenly, × in (no) wise.
So… Why is your interpretation correct?
The Hebrew is, literally, die-die (muwth-muwth) with two different verb tenses (dying and die), which can be translated as “surely die” or “dying you shall die.” This indicates the beginning of dying, an ingressive sense, which finally culminates with death.
muwth
I’m responding specifically to the JW doctrine. You bring up good points for anyone who wants to dig in deeper.