Scouring of the Shire—how old is it?

Tolkien's earliest written reference to some form of the Shire being destroyed dates from about August 1939, when the narrative had reached Rivendell, but Tolkien had yet to write the Council of Elrond

In a footnote to the section devoted to the Scouring chapter in Sauron Defeated, Christopher sums up some of the earlier references to the Shire's destruction.

It is interesting to look back at early references to the destruction in the Shire. In a note probably belonging to the time of the outline 'The Story Foreseen from Moria' (VII.216) my father wrote: 'Cosimo [Lotho] has industrialised it. Factories and smoke. The Sandymans have a biscuit factory. Iron is found'; and in the earliest reference to the Mirror in Lothlorien Frodo was to see Trees being felled and a tall building being made where the old mill was. Gaffer Gamgee turned out. Open trouble, almost war, between Marish and Buckland on one hand - and the West. Cosimo Sackville-Baggins very rich, buying up land' (VII.249; cf. also VII.253, where there is a reference to the tall chimney being built on the site of the old mill).

Looking at these references (and others from The History of Middle-earth) individually:

• From "an isolated page" written prior to the Council of Elrond: (The words in brackets are words that Christopher said were very illegible and he wasn't sure about).

  What of Shire? Sackville-Baggins [?his friends hurt] lands [?There was war between] the four quarters.

• From a scrap of paper Christopher associates with an outline written around the time of The Mines of Moria:

  On the same scrap are notes referring to the Shire at the end of the story, when Frodo and Sam returning find that "Cosimo [Sackville-Baggins] has industrialised it. Factories and smoke. The Sandymans have a biscuit factory. Iron is found.'

• And from a later addition to the above mentioned outline:

  [Chapter] XXVIII What happens to Shire?

• From an outline of the Mirror of Galadriel scene written shortly before that chapter itself.

  King Galdaran's mirror shown to Frodo. Mirror is of silver filled with fountain water in sun.

  Sees Shire far away. Trees being felled and a tall building being made where the old mill was. Gaffer Gamgee turned out. Open trouble, almost war, between Marish and Buckland on one hand - and the West. Cosimo Sackville-Baggins very rich, buying up land. (All / Some of this is future.)

• And then from Tolkien's first written version of that passage. (Written after writing the chapter, but before starting the next.)

  (Put in Sam's vision of the Shire before the ring scene.)

  Sam saw trees being felled in the Shire. 'There's that Ted Sandyman,' he said, 'a-cutting down trees that .shouldn't be. Bless me, if he's not felling them on the avenue by the road to Bywater where they serve only for shade. I wish I could get at him. I'd fell him.' Then Sam saw a great red building with a tall [?smoke] chimney going up where the old mill had been. 'There's some devilry at work in the Shire,' he said. 'Elrond knew what was what, when he said Mr Brandybuck and Pippin should go back.'

  Suddenly Sam gave a cry and sprang away. 'I can't stay here,' he said wildly. 'I must go home. They're digging up Bagshot Row and there is the poor old gaffer going down the hill with his bits of stuff in a barrow. I must go home!'