Hi there, @Rudybatt.
It's my pleasure to help share information about running the 1099 Detail Report in QuickBooks Desktop.
The 1099 Detail Report shows the transactions with mapped 1099 accounts, vendors eligible for 1099 and those vendors who reaches the threshold. It's possible that the transactions reaches with mapped 1099 accounts and those who reaches the threshold are only in the month of September to December.
You may need to check the transactions to see why it didn't reflect on the month of January to August. For additional reference, you may check this article: How to create 1099 summary or detail reports.
Keep me posted if you have any other QuickBooks and 1099 concerns by adding a comment below. I'm just a post a way and always here to help you. Have a great day!