Your thought that the leaves were burned last summer is accurate.  But, instead of the leaves developing new spots this spring, the previously damaged areas are continuing to degrade.  Even so, the green portions of the affected leaves will remain green and healthy.

Recall that this past summer had some unusually bright, sunny days with high temperatures and low humidity. The first image shows varying degrees of sun damage.  The leaf towards the upper left had minor damage, only enough to discolor the leaf.  The thin gray spots on other leaves indicate more severe damage in that the leaf tissue was killed. It’s typical that the gray spots disintegrate and  fall out with time; other times tiny black specks develop in the grayed areas which indicate that a fungus is further degrading the dead tissue; that fungus won't affect the healthy green portions.