I know it's too late to help anyone, but new for ACG2019 were $10 Matchplays at the downtown Boyd properties (Cal, MSS, Fremont). When we visited on 12/26, we were told that the coupons were not valid until 1/1, that they didn't have codes to enter into the computer so there was nothing they could do. These were the only casinos where we ran into this - everyone else took the 2019 coupons in late December 2018, including the Boyd properties of Orleans and Gold Coast (which have had MP coupons in the book for several years, and always take them before 1/1).
We also saw that the "earn 200 points, get a free buffet and keep the points" coupons at Boyd properties in ACG2018 were affected by the change to their stupid "tier credit" system (where new cardholders can't earn actual points). Gold Coast honored their coupon for earning only 1 tier credit, and Sams Town for 20 tier credits. (The 2019 coupons all require 40 tier credits.)