After moving a Drupal 6.x site to a new server, I've found that a CCK date field being used by multiple content types is not displaying the values that are stored in the database for the field OR the default value as defined under content management and date field when creating a new node. The field is just blank. For stored nodes, the values are still there when viewing the node, they just disappear when editing it.
I've found two similar issues, but both relate to multilingual support in Drupal 7: 1. Why some fields values are getting empty when editing a node? 2. https://www.drupal.org/node/1146056
ANSWER: I upgraded the Date API module to 6.x-2.10 and the problem was fixed.