Scholar, the punishment is for israel but their punishment only makes up part of the 70 years. I feel that a lot of the trouble with JWs understanding this account is due to the misleading NWT translation. The Nations who "serve" babylon doesn't start with Jerusalem. For example, see below
Jeremiah 25:17,18
NWT: So I took the cup out of the hand of Jehovah and made all the nations to whom Jehovah sent me drink: 18 starting with Jerusalem and the cities of Judah, her kings and her princes, to make them a ruin, an object of horror, something to whistle at and a curse, as it is today
ESV: So I took the cup from the LORD’s hand, and made all the nations to whom the LORD sent me drink it: 18 Jerusalem and the cities of Judah, its kings and officials, to make them a desolation and a waste, a hissing and a curse, as at this day
Jeremiah 25:29
NWT: For look! if I am bringing calamity first on the city that bears my name, should you go unpunished?
ESV: For behold, I begin to work disaster at the city that is called by my name, and shall you go unpunished? You shall not go unpunished, for I am summoning a sword against all the inhabitants of the earth, declares the LORD of hosts.’
As you can see above NWT adds starting and first to give the reader the impression that the 70 years begins with Jerusalem. Very sneaky