As R_M says - and you obviously had noticed too, T - smartie is an accepted word, and was playable in that puzzle. A few dictionaries list smartie as an alternate form of smarty, and some authors have used that spelling, as revealed for example, by a search at Project Gutenberg. So I think we certainly should retain smartie.
Should we allow smarties as well? There are precedents, with other word pairs where the -IE word is much less commonly used than the -Y word. One example is candies.
But in this case, I'm not sure if smarty is such a dominant spelling compared with smartie. (The singular of the chocolate Smarties seems to be "Smartie", but that's probably not relevant, as I don't think this brand name has come into usage as a generic word.)
Any other thoughts on this?
