The market forecast does not dynamically account for market sort count changes. The numbers get scaled based on the herd size, so until the population changes after the sort, the numbers don't get affected by the market sort count.

For example, the market forecast says you will have 200 market pigs in 5 days. You sort 50 market weight pigs today. The forecast will continue to say you will have 200 market weight pigs tomorrow, you have sorted 50 of the expected 200 so far, but those pigs are not removed from the market forecast until the market sort is completed and the population is adjusted.