Prior to the discovery of the Dead Sea scrolls, the oldest Hebrew copy of Isaiah was completed about 900 AD. It is part of Codex Leningrad which is the oldest copy of the Masoretic Text. The MT is the official Hebrew version of the Holy Scriptures of Judaism. It was copied, edited, and distributed by a group of Jews known as the Masoretes between the 8th and 11th centuries AD. Original Hebrew had no vowels but the Masoretes added vowel points as a guide to correct pronunciation.
The Dead Sea scrolls were discovered between 1947 & 1956 in caves near the ruins of ancient Qumran. One of the scrolls was a copy of Isaiah dated to 100 BC. It is the oldest copy of Isaiah in existence and is very similar to Masoretic Isaiah from Codex Leningrad with the exception of the vowel points. Also found were a tattered copy of 1 & 2 Samuel and fragments of every book in the Old Testament (Hebrew Canon) with the exception of Esther.
The Greek Septuagint text was translated from the Hebrew Scriptures in the 3rd century BC. The oldest copies of the LXX are Codex Sinaiticus and Codex Vaticanus. Both are dated to the 4th century AD and both contain a copy of the book of Isaiah.
Some believe Septuagint Isaiah was translated as early as 285 BC while others believe it was completed closer to 200 BC. That would make it at least a century older than the Great Isaiah Scroll from Qumran.
During the period between Septuagint Isaiah and the Great Isaiah Scroll, the standards for making copies of the Holy Scriptures of Judaism weren’t as stringent as those of Rabbi Akiba, at the beginning of the 2nd century AD, and those of the Masoretes much later. Therefore, it is possible that the Hebrew word “bethuwlah” (literally meaning “virgin”) was used in the Hebrew text of Isaiah 7:14 in the 3rd century BC and earlier.