1005C report line 14 coding for Marriage/Divorce/Decline to PPO tier changes

We understand new hires and terms now. How does it work for Marriage and  Divorce that occurred in the middle of the month for Line 14?

1. Let's say, I am single, and married on Feb 16th, Jan 1B, Feb 1D or 1B?

System shows that  1B for Feb even though electable choices are 1B and 1D?  Why it is not showing 1D for Feb?

2. On the other case which is correct but behaving differently,  So Employee divorced on March 19th?  It shows Jan 1E, Feb 1E, Mar 1C which is correct.  Electable choices are 1B, 1C.  

Basically, per our company, dependents are covered all partial month in either marriage or divorce case or birth child, decline to PPO coverage. How does the line 14 coding work for partial month tier changes? What is the rule of thumb?