Though some WT publications have said something to the effect that "the Earth might be as old as scientists say" and/or that "the universe might be as old as scientists say', at least one WT publication specifically said some undisturbed rock formations on Earth are billions of years old and at least another WT publication said the sun is billions of years old. Note the following examples.
Paragraph numbered 13 on page 10 of "Life Does Have a Purpose" (copyright 1977) says "Yet for billions of years, with apparently little or no change, the sun has steadily produced light and heat.' Paragraph number 7 on page 8 of the same book says "The heavenly bodies have revolved in their vast orbits at tremendous speeds, with astounding precision, for untold millions of years." [The italics are that of the book, not mine.]
The book "Reasoning from the Scriptures" (copyright 1985, 1989) on page 88 under the main heading of "Creation" says:
"Was all physical creation accomplished in just six days sometime within the past 6,000 to 10,000 years?
The facts disagree with such a conclusion: (1) Light from the Andromeda nebula can be seen on a clear night in the northern hemisphere. It takes about 2,000,000 years for that light to reach the earth, indicating that the universe must be at least millions of years old. (2) End products of radioactive decay in rocks in the earth testify that some rock formations have been undisturbed for billions of years." Regarding the word "day" used in Genesis chapter 1, the next paragraph says 'The term used allows for the thought that each "day" could have been thousands of years in length.'
The WT brochure called "Was Life Created?" (copyright 2010) while denying evolution, does teach progressive creationism on page 27. There it says:
"The Bible's narrative allows for the possibility that some major events during each day, or creative period, occurred gradually rather than instantly, perhaps some of them even lasting into the following days.*
ACCORDING to their kinds
Does this progressive appearance of plants and animals imply that God used evolution to produce the vast diversity of living things? No."
BluesBrother, that you quote you gave from the Watchtower 2015 1st June is fascinating. I am surprised that the WT said such. It seems that in the print edition the quote appears somewhere within pages 3 - 5. It can be read online at https://wol.jw.org/en/wol/d/r1/lp-e/2015402 . Besides saying the words you quoted the article also says:
"Scientists estimate that the earth is about 4 billion years old and that
the universe was born some 13 to 14 billion years ago. The Bible sets
no date for the creation of the universe. In no place does it affirm
that the earth is only a few thousand years old. The very first verse in
the Bible reads: “In the beginning God created the heavens and the
earth.” (Genesis 1:1) That general statement allows scientists to determine the age of the physical world according to sound scientific principles." [Note: Instead of about 4 billion years, the scientific estimate is more accurately stated as about 4.5 billion years old for the age of the Earth.]
Sea Breeze, though Genesis 1:14 in the NKJV says "... for signs and seasons, and for days and years" and thus expresses the wording you stated of 'so that there could be "seasons, days, and years', some other Bibles (though ones less literal) express the idea of signs marking the time frames. Note that the REB (copyright 1989) says "... serve as signs both for festivals and for seasons and years." The HCSB (copyright 1999, 2000, 2002, 2003) says "serve as signs for festivals and for days and for years." The NIV (1984) says "... let them serve as signs to mark seasons and days and years" and the TNIV of 2005 says the same The NLLT (1996) says "... will be signs to mark off the seasons, the days, and the years." The NAB (copyright 1970 for the Genesis), a Catholic Bible not to be confused with the Protestant NASB, says "... Let them mark the fixed times, the days and the years".
Whether the passage means 'for signs, season, days, and years' or whether it means 'for signs of seasons, days, and years' I don't know for sure, especially since since I can't read/translate ancient biblical Hebrew and ancient biblical Septuagint Koine Greek. It would be helpful to know what the specific wording is in the corresponding Babylonian and Assyrian creation accounts since the ancient Jews/Israelites were in captivity in Babylonia for a time and later many lived in Persia for a time, and it appears that the the Jews/Israelites adopted the cosmology of those ancient civilizations.