Issue 1/
completion is not used at all for database and scorm module. For assignments using due date make sense, but for database completion info should be used over 'available to' date.

Issue 2/
Available to and from behaviour seems odd. When both are set in future, the close date is shown to user. This kind of indicates the module is open. I would suggest to show open date until that date is in future and then close date after that.

Issue 3/
For SCORM module, when both are set in the future, the "due date" is shown, but if only the "available from date" is set, then it's that one that's used, leading to probable confusion (with bad results if student expects date to always be the "available from" one and misses deadline). A label would be good.