Translation is not an easy task and errors have occurred, even hundreds. For example, the King James Version has over the centuries been corrected or improved uncountable times. Surely also in other Bible translations. As the centuries passed, the importance of Latin became increasingly important. The Bible was forbidden to ordinary people. It was only in use of the clergy and scholars (who were often theologians as well).
In the old Greek scriptures translated in English before the first millennium, the words “everlasting,” “evermore,” “forever and ever” or “eternal” or the like were not used. Because I am not a linguist, I do not intervene in history in more detail. I can only say that maybe since the 1300s, there was a change in translations and that, the characterization of eternity became more common and became exclusive.
I have not been able to review the early Middle Ages Bible translations, but Wyclif 1382 has not translated “for ever and ever” but “into Worlds of Worlds”, which I think refers to (the world) eras. They may be long, but not necessarily “for ever and ever”. John Wyclif completed his translation in 1382. Just over a hundred years later William Tyndale’s 1536 Bible translation, then Myles Coverdale (1539 The Great Bible), Thomas Cranmer’s Book of Common Prayer (1539), the Geneva Bible (1557), Rheims (1582 ), and The King James Version (1611 translations), “forever and ever” “everlasting” and “eternal” became more common and are still the mainstream interpretations of today.
Rheims: Mark 3:29 But he that shall blaspheme against the Holy Ghost, shall never have forgiveness, but shall be guilty of an everlasting sin. KJV: “eternal sin”.
Jhn 3:16 For God so loved the world, as to give his only begotten Son: that whosoever believeth in him may not perish, but may have life everlasting.
Tyndale: Jhn 3:16 For God so loveth the worlde yt he hath geven his only sonne that none that beleve in him shuld perisshe: but shuld have everlastinge lyfe.
Tyndale: Rev 2o:10 and the devyll that desceaved them was cast into a lake of fyre and brymstone where the beest and the falce prophet were and shalbe tormented daye and nyght for ever more .
Geneva Bible: Rev 20:10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet [are], and shall be tormented day and night for ever and ever.
The vast majority of contemporary translations also use the terms from the Middle Ages:
NASB Rev 20:10 And the devil who deceived them was thrown into the lake of fire and brimstone, where the beast and the false prophet are also; and they will be tormented day and night forever and ever” (εἰς αἰών αἰών).
King James translation is a translation based on the Latin language, as well as all the translations that follow it. After the seventeenth century, KJV has been restored countless times and perhaps hundreds of translation items have been improved. My own writing uses several modern translations as well as KJV translation. When I compare, for example, three modern translations, I often have to say that the differences between them are in word choices to separate a translation from previously published translations. I prefer to use contemporay language; instead of saying ” It is the Spirit which quickens” I choose a translations which says ” It is the spirit who gives life”. The truth is spelled out over time and with the refinements of the translations.