80 Percent Completion Time
The time within which USCIS finishes 80 percent of cases for a form. The number the official tool actually shows.
When the official tool shows a number, it is the 80 percent completion time. That means 80 percent of cases like yours finished within that period. It is not an average and not the longest a case can take.
So if the tool says 10 months, two out of ten cases took longer. Yours might finish faster or land in that slower 20 percent. It is a benchmark for what is typical, not a date you can count on.
This is why a case can pass the posted time without anything being wrong. Verify yours at https://egov.uscis.gov/processing-times.