A typical household sewer line isn't full of water. And, what's there is (hopefully) flowing so there's little to no pressure on things. The casting may have been a little rough. If it was mine, and I know I tightened everything up to spec upon first installation, I probably wouldn't worry about it. Hopefully, one of the pros will chime in to confirm or deny my thought. It's possible that over that year, things moved a little through expansion/contraction cycles and maybe settling. If I had access, I'd consider just retorquing things, but if I couldn't, I wouldn't lose sleep over it.