Longines 63720E is the reference in this note. Treat the papers and the box as a separate object from the watch. The card should repeat the reference you can read on the case. If it does not, believe the case until you have a reason in writing, and record the mismatch. Count the links or look at the strap holes. Extra holes, a shortened bracelet, or a strap that is not the width of the lug gap are changes people make so a watch fits. They are worth writing down because the next owner needs the same fit. Look at the spring bars. Bent tips and rust at the lug hole tell you the strap has been wet or forced. The crystal, the insert, and the hands are the other parts people replace when they want the watch to look newer than the case. Compare the finish of those parts with the finish of the lugs. Same wear, same age. Different wear, a later part. That comparison is the whole of a used-watch note.
How it differs
Longines 63720E should be checked as one case, one dial, and one bracelet or strap. Measure the width and the lug-to-lug distance. Read the engraving. Then see which part looks newer than the others. People change crystals, inserts, clasps, and straps. The case is the part that should still match the reference you wrote down.
What to check on a used piece
What to check on a used Longines 63720E starts with the engraving. The reference to read is 63720E. Then check end-link play, clasp fold, and whether the hands pass each other. There is no price in this note.
Common mods
Common changes are the strap or bracelet, the crystal, the clasp, and sometimes the hands. Write which of those looks newer than the case. Leave the reference name tied to the engraving.
What people change
On the Longines 63720E, people change the bracelet, the case, or the movement.