Right. And knowing the typical length of factory choke tapers helps too. Open or no chokes and short choke tapers may indicate either shortened barrels or choke reaming. Another clue is the position of the sight bead. Many butchers who shorten gun barrels seem to have trouble getting the bead centered or the correct distance from the muzzles.
The example in the photo above seems to show a "keel" below the solder that may or may not be integral with the bottom rib. Without factory records, factory letter, hang tag, or original invoice, it can take some examination of all the evidence to arrive at a conclusion.