On the Select your 1099 vendors page of the QuickBooks 1099 Wizard (Vendors > Print/E-file 1099s), check that all the vendors for whom you want to prepare Form 1099-MISC are on the list and have a checkmark showing in the Create Form 1099-MISC column.
QuickBooks also shows you the account you used to pay this vendor during the year (from your chart of accounts). If you paid this vendor from more than one account, Multiple appears in the Account Used column.
Working with 1099s
Troubleshooting 1099 information