Ann: Rincon Lithium Project - Progress Update, page-95

I was actually thinking about this yesterday as well.

If 18 months is a period which started the moment the chart started it descent from the plateau of 580k CNY (12 months ago), then in 6 months from now we should see a reversal in the li2co3 price chart.
Note that we are then at a bottom, so it's not the end of low prices, but a change from surplus to deficit and hence a reversal in sentiment as well.
This reasoning still holds true if the time period for low prices needs to last 18 months, as when the price rises, it still will be on the lower side, and hence before prices will be considered high again, we might be 18 months further from April 2023.

Just my take how I look at it