It depends on which unit your original cow tag was for. Colorado hunting tag structure denotes every tag "List A, List B or List C." You can have an A+B or B+B for a given species. List C is unlimited but generally for management or damage areas and often private land only. In fact, I believe for elk this year there aren't any List C available. But don't quote me on that.
Example:
1) I had an over the counter either sex archery tag for my list A.
2) From the leftover list I got a cow tag for Unit 54, First season.This tag was list B.
If this is still a little confusing, let me know which unit your ML cow tag was for and I'll let you know for sure. Good luck! -Bryan