Mammo shows asymmetry at superior in breast seen only on mlo view. Spot compression view reveals asymmetry dispersed into normal glandular tissue.?

Normal. Abnormal breast masses will not compress out but imaging artifact will. All imaging studies have a multitude of technical reasons why one single view could show something that really isn't there at all. Multiple views and other techniques like spot compression will tend to give a better picture of equivocal findings.
No worries. Sounds like you had a questionable area on a screening mammo, came back for special diagnostic views for further evaluation, and it was determined that it represented normal tissue. This is a common scenario. Sometimes pockets of normal breast tissue randomly get superimposed on one another on the mammo, making it look like an abnormality might be there. The extra views clear it up.
Congratulations. This is a common reason for being called back for additional mammographic views. Since the mammogram is a 2 dimensional exam of a 3 dimensional structure, tissue overlap or normal variations in tissue density can create a false or pseudo mass. The recent development of 3-d mammograms is helping to address this issue and many facilities are adopting this technology. Ask if it is available near you.