First, the Jehovah's Witness teaching that there was a time when Jehovah God was utterly alone, before he created - as the first and only direct creation he ever made - the Word of God, also known as the Son of God - goes back long before they produced their New World Translation of the Bible. This is subtly significant, as will be shown later.
The very earliest record of that teaching may be long before these old ones I am aware of. This is from a book I have in front of me, published in 1956, before their New World Translation came out. The quote is from Thomas James Sullivan, Director and Superintendent of [JW] Ministers and Evangelists, based at the then HQ in New York. He had already been serving for more than 12 years as a director of the Watch Tower Bible & Tract Society. Those are his credentials, and what he says on this topic is in agreement with JW answers here:
"Psalm 90:2 states that God Almighty, the Father, Jehovah, is from
everlasting to everlasting - without beginning. Jesus, in Revelation
3:14, identifies himself as the beginning of God's creative works.
Hence Jesus could not be co-eternal with his own Father." Jehovah's
Witnesses, p.161, Marley Cole, George Allen & Unwin, 1956
"God is the source of all life outside of himself, Psalm 36:9... The
prophet Moses recognized that the living God had no beginning, even as
he will have no end (Psalm 90:1,2)... The ever-living God was before
even such heavenly creation, and at that time he was all alone. What
did he create first? ...he started with the highest form of creature
life, a heavenly one. He made it the best living creation in all
existence... This first creation of God came to be called 'his
only-begotten Son.' John 3:16... He was the beginning (not, beginner)
of God's creation, so that God's creating of creatures began with this
Son. Jehovah stands out as the One Creator and all other things are
what he created... Proverbs 8:30 quoted Wisdom personified as saying,
'I came to be beside him as a master worker.' So the wise
'only-begotten Son' of God became a master worker beside the great
Creator Jehovah God. His heavenly Father did not leave him idle but
used him in the producing of all other things living and lifeless."
Things in which it is Impossible for God to Lie, pp. 119, 120, 122, 126., published 1965
The Jehovah's Witness stance on Isaiah 44:24 is stated in their book Isaiah's Prophecy, under the heading 'The Climax of the Test of Godship'. It starts this section by saying verses 24 to 28
"brings Jehovah's legal argument to a powerful climax. He is about to
present his own answer to the severest test of Godship - the ability
to foretell the future accurately... the one and only Creator, the
sole Revealer of the future and Israel's hope of deliverance. The
passage rises in a dramatic crescendo to the announcement by name of
the man who would liberate the nation from Babylon." Isaiah's
Prophecy, Vol. II, pp. 70-74, published 2001
There is not a word of explanation about verse 24 in those 5 pages. But it does clearly stick to the long-held belief that there is only one God, who alone created everything, so that fits in with Jehovah's Witness insistence that they agree with Isaiah 44:24.
The crux of the matter then becomes their view of Colossians 1:15-16, and this is where their NWT is vital to make them say those verses are not problematic. The NWT came out just before 1960 and says of Christ in their Interlinear of 1969:
"...by means of him all [other] things were created... All [other]
things have been created through him... he is before all [other]
things and by means of him all [other] things were made to exist... to
reconcile again to himself all [other] things..." The Kingdom
Interlinear Translation of the Greek Scriptures, p. 896, 1969 edition [square brackets theirs]
Square brackets denote a word added to the text that was not in the original source. No other translations add the word 'other' to those verses, not even once, let alone five times. The reason for those additions in the NWT is that it gives the impression that Christ is not before one other - namely, Jehovah. He is before all things other than Jehovah. This makes it easy to then claim that Colossians 1:15-16 is not a problem when viewed alongside Isaiah 44:24. Yes, Jehovah alone created everything, they agree, because the Son was but an 'agency', or 'channel' through whom God created everything else.
This needs to be included in any reasoning Jehovah's Witnesses make regarding Isaiah 44:24. Because of their NWT rendition of Colossians 1:15-17, they actually don't see any difficulty holding the two texts together. They continue to elevate Jehovah as supreme, above his Son, and the Son in a secondary position because this Son had a starting point in time (unlike Jehovah) and no praise is to go to Jesus regarding creation. However, if those five added words were kept out of those verses, they might see that the problem remains as stated in the question. As it is, they don't even credit Jesus with being a co-creator.