The Searcher - interesting verse. Just did some research on it to find the Societies view:
DOES ISA 7:14 REFER TO A 'VIRGIN' OR A 'YOUNG WOMAN'?
(Isaiah 7:14) Look! The young woman will become pregnant and will give birth to a son... (NWT 2013)
(Isaiah 7:14) Look! The maiden herself will actually become pregnant, and she is giving birth... (NWT '84)
YOUNG WOMAN - w54 6/1 p. 351 Questions From Readers
It is true that ‘al·mah′ does not necessarily mean “virgin” the way the Hebrew word b e thu·lah′ does.
The divine Author of the Hebrew Scriptures doubtless had a purpose in using the Hebrew word ‘al·mah′ at Isaiah 7:14 instead of b e thu·lah′ (“virgin”).
VIRGIN - w97 8/15 p. 9 Part One—How the Bible Came to Us
For example, at Isaiah 7:14 the Septuagint used a Greek word meaning “virgin,” referring prophetically to the mother of the Messiah.
YOUNG WOMAN - w11 8/15 pp. 9-10 par. 8 They Waited for the Messiah
The Hebrew word bethu·lah′ means “virgin,” but another term (ʽal·mah′) appears at Isaiah 7:14. There it was prophesied that “the maiden [ha·ʽal·mah′]” would give birth to a son.
BOTH! - w13 11/15 p. 17 Seven Shepherds, Eight Dukes—What They Mean for Us Today
The Hebrew word translated “maiden” at Isaiah 7:14 can mean either a married woman or a virgin.
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