2 jobs one employer/ Employement letter starting date?

各位大俠：
I have been in two positions since started working for the current employer. first position start in 2002, the other started in 2005. I am using this 2005 position to apply the green card. When I ask the employer to write the "employment letter", what they should state the starting date? 06 or 04? Attorney say doesn't matter. I am Worry about it will effect the result. Please help!

Many many Thanks!