Rashi actually did travel pretty much. He mentions his being in ‘Rusia’, and he gives a word from that language. By the building of the Beis Hamikdash by Shlomo Hamelech, Rashi writes by the word Yekev, dluta Berusia.
I can’t tell you about Spain, but when he defined a word it wasn’t from lack of knowledge, or from the process of elimination. He had a reason or a Mesora to define it as such. Which serious person would say, I only know of a few other grains so this must be it? Isn’t that the complaint against the Tcheiles? (There, at least he depended on the fact that he did research.)