Workbook2.xlsx
In this workbook I have created 2 combo boxes (using data Validation) 
First Combobox values: Month, Quarter, Year
Second Combox Values changes based on the selection for first combobox: 
Month: Jan,Feb,Mar etc.
Quarter: Quarter 1, Quarter 2 etc.
Year: None
Through Connections I have created Workbook connection to 2 other workbooks (Workbook1.xlsx) and (Workbook3.xlsx) which will be data source. 
Workbook1.xlsx
Description     dateEntered     dateCompleted
1234 green     01-Jan-17        01-Jan-17
2345 purple    10-Feb-17        11-Feb-17
1256 orange   02-Jan-17        01-Feb-17
3456 black      01-Jan-17        11-Apr-17
7890 yellow    06-Feb-17        11-Feb-17
9876 white     02-Mar-17       12-Mar-17
Workbook3.xlsx has multiple tabs for example:
TabName: TBD January 2016
TabData: 
January 
2341
3456
4567
TabName: TBD January 2017
TabData: 
January 
9876
1256
TabName: TBD October 2017
TabData: 
January 
7890
what I have to now is link the value From second Combobox to dateCompleted (Workbook1.xlsx) to show the following calculations and data only if the first 4 characters (alphanumeric) matches the data in any of the tabs in (Workbook3.xlsx)

Stats needed (for instance if January is selected in the second Combobox): 
Number of Entries in January: 2 ('1234' will not be counted as it does not exists in any tab Workbook3.xlsx)
Number of Completions in January: 1 (count of dateCompleted of that month)
Average(days): dateCompleted for that month - dateEntered for that month/(# of dateEntered for that month)
Data set to look like:
Description     dateEntered     dateCompleted       TBD
1234              01-Jan-17        01-Jan-17              TBD January 2017
Any help is appreciated. I'm new to Excel and trying to figure how to do this.