The NUMBERS-TEF files are created when Apple iWork Numbers spreadsheet software saves the spreadsheets to iCloud. Whereas, Numbers spreadsheets saved on the local computer use the .numbers extension.
Difference between NUMBERS and NUMBERS-TEF
The NUMBERS-TEF files are the similar spreadsheet like .numbers. Both files can be created by using Apple iWork Numbers spreadsheet software. Please note that the Apple iWork Numbers is included in the iWork Productivity Suite. The NUMBERS-TEF is just a suffix -TEF added to Numbers documents when saving them to iCloud for use on an iOS device, or another Mac.
The Mac OS or iOS versions of Numbers open the .numbers-tef without any issue. The spreadsheet will load properly just like as .numbers file.