Hi -
As it relates to your salary, have they all been paid in the same currency? Then you could approximate for each given period based on historical exchange rate. If it becomes very complicated given different exchange rates and does not show the trend it should, then I would contact the admissions committee anonymously and ask how they would like this information presented.
As far as organization numbers, you can state a 10,000+ number for a very large company. For Junior Achievement, I suppose it depends on if you are trying to categorize the organization nationally or just in your region/center/groups. These numbers matter in the sense that you don't want to misrepresent the truth, but you just need to present accurate information based on facts that are easily available.
I hope this helps.
Erin
Erin Schuhmacher
Senior Consultant
mbaMission
http://www.mbamission.com