Well, there is certainly disagreement with the view that 2018 supercedes 2017 here.
http://www.rugbyrefs.com/showthread....rent-from-2017
#8
"The acid test is, will you referee something differently using the 2018 Law Book, from how you would using the 2017 Law book? The answer to that is, no."
#10
"I've not looked at any of the threads on simplified law book as I've heard nothing official from my society"
And that there is no concurrency in place
http://www.rugbyrefs.com/showthread....rent-from-2017
#33
"2018 is a simplified interpretation of 2017 and they will co-exist until a newer amended version comes out"
#78 & #79
"The 2018 Laws are now on world rugby website", AND
"The laws site also lets you access the 2017 version"
didds