That's neat, I never realized that happened.
I am pretty sure articuno/dos/tres are coded to appear in the first patch of grass you walk in after beating E4 since that has always been the case for me. Would also be fairer, since how are you supposed to find it without a map...
Is it safe to save in the Lumiose City Pokemon Centers?
I saw Articuno but it flew away before I even got to do something :/