I only know from experience with 1 terrier that the changes can occur at any time. Coco started as a soft fur dog, grew terrier wires which gradually thickened as he matured. Probably about age 10 it did a recovery thing where he shed and grew it back.. Then as he aged over the last few months of his life he thinned out and became soft again.
Has there been any changes to food or environment?? (Maybe he's growing in his Best Man's coat for the wedding
)
Has there been any changes to food or environment?? (Maybe he's growing in his Best Man's coat for the wedding