The All Souls Deuteronomy (4Q41) isn’t a straight copy. It’s an excerpted liturgical text, and its Ten Commandments reads differently from both Exodus 20 and Deuteronomy 5, including a longer Sabbath command.

That is accurate. 4Q41 is an excerpt collection, probably for devotional use, and its Decalogue blends the Exodus and Deuteronomy forms. The honest description is the oldest surviving text of the Ten Commandments in an excerpted and slightly harmonized form. The harmonization itself is telling: scribes working from both books presupposes that both were already fixed enough to harmonize, which supports rather than undermines the stability of the underlying texts.