Hello, I am lost and could need some help!

I have one variable, lets call it X, which includes living situation (alone, with one other person, with 2, with 3, etc) but this variable only exists in datasets 2000 and 2001. Then I have variable Y, which is the exact same thing, but in data sets 2002, 2003, 2005, 2006, 2008, and 2010. I have already appended all data sets into one. How do I merge variable X and Y to create one variable? ( I am looking for the coding I can write into STATA pls!)
Thank you!