Several sources state that these ringed Soldiers were built from 1992 to 2002 with some sources stating that they could only find 94, 95, x , 97, 98 and 99 stamps.
From auction data over the last 5 years (over 5000 auctions of Model 1961 Soldiers), keyring soldiers are known to exist for all years from 1994-2000. 1993 is a big transition year for soldiers where almost exactly half (48%) are the old design with thick caplifter/canopeners and hollow tail rivets and half are the new design with thinner openers and solid tail rivets.I have never seen any old design (i.e. pre-1993) soldier with a keyring attachment. Typically if you wanted a keyring or lanyard on these you'd just attach a bail to the hollow rivet (a relatively common occurrence). For the 1993 new design solid rivet soldiers, I have not seen any with a keyring attachment.