I just subdivided the short perpendicular edges along the bottom floor of this object and now when I alt. lmb the edge along the long bottom edges (next to the red line along the sides) it only connects up to the next subdivision instead of the entire edge line. Is there a way to re- merge all the vertices along the bottom edges so I can connect the entire edge using alt. lmb? I've tried merge by distance with alternative variables to no avail. Any help most welcome!
Unfortunately, with that topology, the edge loop selection will always be limited to sections between "quad-poles" (as far as I know). However, there's a good chance you can eliminate some of the tedium of selecting all the edges manually by using "Select Similar". Try with different constraints, if necessary. If there are varying sections of your edge loop (such as varying lengths, like the inner curve being shorter than the outer curve, for example), you may want to select multiple sections of different sizes (yes, this can be done), before you choose the Select Similar, to make sure you get them all.