I found this answer to my question regarding marking spouses in v01n200 from 16 June 1999:
One of the things I learned about marking cards based on a relationship, is that the spouse of the relative does not get marked. I understand why this is, but if you don't realize it, and make a gedcom, it is somewhat disappointing to see that all of your relatives are single parents. Once you have marked the ancestors (or descendants) of a couple or individual, take one more action.
1. Go to Find Anything 2. Select Couple card 3. # of Marked Spouses is 1 4. Mark the cards in the list produced.
Now your gedcom will include spouses of the relatives you originally marked.