There's probably NOT been any change is status, rather a universal designation that will keep the database functional.
Imagine the confusion if a colt was listed as such, then next time as horse and later as a colt?
I looked at the Pathway FAQ and the only explanations are in regards to Pathway-itself.
Best chance of any clarification would be to contact David Carr or Anne Chunko of the USTA. You may even call them by looking the USTA Contacts page.