"percent-used" ("percentage-size-used") is calculated differently on different versions of ONTAP.

Hello.
I have noticed some deviation in value of Volume "percent-used" value for volume show command on different C-Mode ONTAP versions. It is also true also for ZAPI volume-get-iter "percentage-size-used" value (which is the same).
What I have noticed:

• On 8.3 and 9.2 "percent-used" =  (Used data space + Snapshot Reserve Size) / Total Volume size
  
• On 9.7 "percent-used" =  Used data space / Data sector Size
  

So, on the latest 9.7 ONTAP calculation made differently.
Could someone tell from which ONTAP version calculation approach has changed? And point the doc where this is mentioned (because I couldn't find this place at least for now).

Thanks!