Assign A Value On A Per Person Basis Based on Date

I have a data set that has an employee's name, a date, and several metrics. These employees can be promoted to new groups based on their skills. I would like to be able to easily run trend analysis based on the these groups and not count an employees stats that they achieved before they were promoted.

Can you advise?

Sample Data File:
Stats 1 Stats 2 Stats 3
1/1/2014 Person A 1 4 4320
2/1/2014 Person A 1 3 4576
3/1/2014 Person A 1 4 3850
2/1/2014 Person B 1 7 5562
3/1/2014 Person B 1 9 6210
1/1/2014 Person C 1 3 2950
2/1/2014 Person C 1 4 3902
3/1/2014 Person C 1 2 2752

Sample Group Assignment:
Date of Assignment login level
2/1/2014 Person B level 1
1/1/2014 Person A level 1
1/31/2014 Person A level 2
12/15/2013 Person C level 2

Additional information: there are three (currently) groups that people can be in (level 1, level 2, and level 3). They could be promoted at any time and they could even skip level 2 and be promoted to level 3.

This is what MS Access is for....summing, collating data with conditional clauses.
Excel is just for summing all.