You sometimes get a lot of nails without shafts and shafts without nails
during re-roofing of buildings, but it's more a function of breakage than
intentional snipping.  The copper-alloy nails are interesting, as they had
limited utility.  They tend to have been used in situations where corrosion
or sparking might be a problem, e.g., ship and boatbuilding, and
construction of powder magazines in ships and fortifications.

There are problems with the recycling argument. If the nails were nailed in
and the heads cut off, the heads would be available for recycling and the
shafts would be left in the wood.  If the nails were nailed through
something thin and cut off from the back side, you might have shafts (which
would not necessarily be bent.  Usually, however, the practice was to
"clench," or bend such nails to hold them in place, particularly in
shipbuilding.

There is another possibility. Some finish nails were made without heads, and
might appear to have been snipped; the wrought ones would probably have been
snipped from the bar stock during manufacturing, and with the cut ones, you
would have the sheared edge of the plate where the head should be. What
sizes are these nails?

Lauren Cook