I've just found the 16/17 playing rules on my PC. Rule 21.11 allowed for reserve day (and which was required). However in subsequent years there is no such rule; the only mention of reserve days is related to grand finals. That may not stop the CSB from raising the possibility with the clubs for this year, but it's not written into the rules. The 16/17 rule only covered Championship and Divs 1-4.