diff --git a/www/conservancy/apps/assignment/models.py b/www/conservancy/apps/assignment/models.py
index 0b8243a62837f2386ddf5c3daf7384fae4adce1d..c06d5717fd24edf89828033bc7435e276f54de71 100644
--- a/www/conservancy/apps/assignment/models.py
+++ b/www/conservancy/apps/assignment/models.py
@@ -4,6 +4,8 @@ from django.db import models
 
 
 class Assignment(models.Model):
+    """A copyright assignment to Conservancy."""
+
     full_name = models.CharField(max_length=255)
     email = models.EmailField()
     place_of_residence = models.TextField(
@@ -20,9 +22,12 @@ class Assignment(models.Model):
         choices=[
             ('up to this year', 'One-off up to and including this year'),
             ('ongoing', 'All existing and new contributions'),
+            ('specific', 'A specific period (details below)'),
         ],
         default='up to this year',
     )
+    coverage_from = models.DateField(blank=True)
+    coverage_to = models.DateField(blank=True)
     attestation_of_copyright = models.BooleanField(
         'I attest that I own the copyright on these works'
     )