Given that it was not published until 1824, it is even possible that Beethoven made further revisions at the time of publication, a period when he was producing some of his greatest works, including the Diabelli Variations, the Missa Solemnis and the Ninth Symphony.
Direct evidence for this comes, among other elements, in the form of the extremely energetic and tight counterpoint of the double fugue in G minor that makes up the transition from variation X to the allegretto finale.
Lockwood suggests that the revision and publication late in life of a project begun in youth should be understood as an act of nostalgia on Beethoven's part, in which "the old composer, profoundly engaged in musical projects of the greatest difficulty and depth, looks back with nostalgia on a simple work from his youth, and seeks to bring it out in the world, having clothed it with just enough complexity to balance its naivete and directness with the wisdom of his later years".
The theme itself, when it finally appears, is almost comically anticlimactic—a simple, even trivial tune taken from Wenzel Müller's opera Die Schwestern von Prag, composed in Vienna in 1794 and popular during Beethoven's lifetime.
Like the introduction, this final variation shows a chromatic and contrapuntal complexity that goes beyond what Beethoven achieved in his early works, and that likely reflects revisions made during his period of greatest maturity.