I have been working with my students on adding suffixes -er, -or, -ist, and -ian. We have been using word sums. All was going well until we tried adding -an or -ian on Asian and Australian. 

Asia/ + an --> Asian or Asi/a/ +ian --> Asian or is it Asia + n --> Asian

Do we actually drop the <a> to add the -an? Or drop the <ia> and add -ian? Or is <n> a suffix?

My students have now compiled quite the list of countries that end in <a> and <ia> and looked at the word sums for each. Most appear to drop the <a> And add -an OR add -n as a suffix.

I cannot find any rule for dropping <a> nor can I find any evidence of suffix -n (although I do remember Peter talking about some structural evidence with grown etc). 

Are we missing something? I would never even have noticed this if we had not been using word sums to think through suffix additions to words.