It’s been asserted that the Sloppy Joe owes its name to the bar SLoppy Joe’s. I thought it was the one in Key West (opened in 1933 under that name), but apparently it probably comes from the one in Havana Cuba (like the one in Key West, freqynted by Hemingway). This web page makes a strong case:
In any event, Google N-gram Viewer has Slopy Joe sporadically showing up earlier, but really starting circa 1920.