Last week's CPI data released marked the biggest "unexpected decline" since 2009, with all 62 predictors surveyed by Bloomberg being proven wrong. Sounds good, but here comes the problem.

The longest government shutdown in history directly messed up data collection. The U.S. Bureau of Labor Statistics (BLS) lacked most of October's price data, which not only affected the calculation of monthly changes but also caused economists to point out that November's data was also discounted. The market simply dubbed the November CPI report the "Swiss Cheese Report"—full of holes.

Here's the key point. The December CPI will be released on January 13, and this data is highly significant. Why? Because it will be published before the Federal Reserve's meeting at the end of January, and the decisions made at this meeting are crucial for market expectations. This report can provide the Fed and traders with a truly clear picture of the economy, no longer relying on guesswork from incomplete data.