What may be missing at this point in the material is a definition for what "indications of a change in trend" we should be looking for.
One of the characteristics is a sharp increase in volume, suggesting outside ("public") participation entering the market. In this case, the outside interests would be buying and "they," the smart money, would be selling into the demand.
In early January, the typical volume was reasonably steady at about 2 million shares and there was no significant increase leading up to the 9th. I think this, coupled with the the observation that volume was beginning to increase on days with low closes and the other items mentioned by Wyckoff, suggest there is little outside buying, indicating a short-term top and not and change of trend. Buying and selling climaxes occur on each time frame in addition to major turning points.
An early issue of the Ticker magazine had as the epigraph: "The Fundamental Principle of Wall Street is the Sale of Securities to the Public" (1908). So an important thing is who has the stocks. If the large interests have most of the inventory, esp. if recently purchased in an accumulation area where the public was dumping stocks, the large interests would have to be doing the selling---but there is little public demand to sell to. There is evidence of buying support 2/16 as the price approaches the accumulation zone, which is about where "Tom, Dick, and Harry" bailed out just the month before and are probably exhibiting "masterful inactivity" until "prices are high enough."
In February the volume increases sharply as the index breaks out above the absorption area, and sustained high volume and mostly horizontal price movement suggests that this is probably the outside demand "they" have been waiting for to realize profits.
The data under the blanked-out part of that graph for February and March looks much like the S&P 500 now, except for the sharp increase in volume.
BTW, thanks for posting that chart with the portion blocked out. It made me realize that I have been looking at a different PDF file that is apparently the 1937 course and not the 1931 material posted by dbphoenix in the sticky.