After Altos R520/R720 has been updated with BIOS R91.6, the BIOS version in BIOS Setup will still be 91.
You could distinguish BIOS R91.6 and BIOS R91 with the below full name of BIOS string in BIOS Setup.

- BIOS R91.6: S5000.86B.10.60.0091
- BIOS R91: S5000.86B.10.00.0091

Also, you could identify BIOS R91.6 and BIOS R91 based on the BIOS build date:

- BIOS R91.6: October 9, 2008
- BIOS R91: August 15, 2008