Rev. 6:6 in the KJV says:
"...a measure of wheat for a penny..."
It was a prophecy about an imment crisis in wheat prices.
Notice three specifics about that translation:
(1) The unit of measure is specified - it was called the "measure" - the Grecian measure (which was more or less equal to one quart, and was the standard unit of measurement at the time of writing);
(2) The currency is specified - it was the "penny" - the Roman denarius; and
(3) The exact price is specified - "one penny".
Now notice how the NIV renders the verse:
"...a quart of wheat for a day's wages..."
Notice three specifics about that rendering:
(1) It made the unit of measurement unimportant, changing it from the Grecian "measure" - to the "quart";
(2) It eliminated any specific currency altogether; and
(3) Instead of specifying the price as "one penny" it broadened the price to "a day's wages" without being any more specific.
The licence taken by the NIV rendering leaves the meaning wide-open for anyone to think the prophecy might be fulfilled virtually anywhere, at any time - regardless of the unit of measurement, the currency, the actual price of the wheat, and regardless of what might be happening elsewhere in the world - so long as in the reader's own locality of concern the price of an equivalent quantity of wheat is equivalent to a day's wages in his location. The problem with that is it makes it virtually impossible to ever really know for sure whether the prophecy has been fulfilled even if we are seeing it apparently being fulfilled before our eyes.
Whereas if we take every point of the KJV translation literally, it means, as John Wesley explained, that:
"This must have been fulfilled while the Grecian measure and the Roman money were still in use; as also where that measure was the common measure, and this money the current coin" [underlining added].
Taking the KJV literally means therefore that the prophecy probably had to have been fulfilled soon after the time of writing and somewhere in the Roman Empire. When the price of one Grecian measure of wheat began selling for one Roman denarius, the readers would therefore know that the prophecy was being fulfilled.
Modern Bible versions such as the NIV may therefore be contributing factors in today's end-times views, and may be a cause of some of today's oft-repeated cycle of failed end-times predictions. But back in the day when the KJV was more widely in use, the standard understanding of many such prophetic passages of Scripture was quite different. Matthew Henry's bible commentary as well as Jamieson Faucett and Brown's commentary agree with Wesley's explanation above.