Related Dates Question

Not sure how to add a new related date correctly in this situation:
 

 Have a meeting on day X.
 

 Have added a calendar item for day X.
 

 There will be a report due a set number of days after day X. Let's say 30 days after date X.
 

 On day X, it turns out there will be a new, 2nd, meeting needed before the report can be issued. Let's call the 2nd meeting day Y. 
 

 With day Y added, the report will be due 30 days after day Y, rather than 30 days after day X.
 

 How do I do the following efficiently and correctly:
 

 Add day Y as a related to date to X, and have the X-plus-30 report-due date "shift" to being related to (keyed on) day Y (no longer keyed on day X), while at the same time keeping all 3 dates related to each other? (X, Y and Y+30)
 

 There is also a real possibility a 3rd meeting date will be needed (let's call it day Z). If that happens, I'd need to key the 30 day report deadline to new day Z, while keeping all 4 dates linked (X, Y, Z and Z+30).
 

 I tried but was unsuccessful.
 

 Thanks in advance.