I sometimes indicate the slide symbol up to a certain note with a line that doesn't particularly say from what exact note to slide from. The reason is that it varies so much. I might slide from a half step below sometimes, and other times from a whole step below or more. So in the TAB that you're speaking of, you don't see what note I'm sliding from in the TAB. But you hear me explain it when I go through the example.
Kind regards/E