I noticed that the total number of questions with a score of 10 or more that my proposal needs just changed from 21 to 24. Which is strange because there are no recent changes in the example questions.
Could it be that the number of questions needed with a score of 10 or more change?
No, the total number of questions needed is still 40. The number you are citing is the remaining number of questions needed. The remaining count can go down if someone down-votes a question below 10, or similarly if folks distribute their votes to other questions. It's a dynamic process.