I know this post is very old, from the early days of Waze in Brazil, but I came across this topic this week.
The Wazeopedia material (link below) came out much later, after 11 years! So, it can be included, provided there is a regulatory sign. If there isn’t one, do not add the speed limit. If you do, it is incorrect.
Private roads/Parking lots 
Speed limits indicated on private properties using regulatory signs may be added to segments. ( Speed limits )
Regards,
ivaldonm | Ivaldo N. Magalhães
AM - PB