The ones with four wires are likely wired for A leads, meaning that a contact is closed to short the black and yellow pair when the phone is off-hook. This is for when they are installed as single-line sets behind a 1A2 system.

The three wire ones are just standard sets. There was a time when party lines required the ringer to be wired separately (or differently), but since everything is bridged ringing now, the green and yellow leads are just connected together on terminal L1 of the connecting block.

Ed Vaughn, MBSWWYPBX