Question
The new leaves in a 5' "Emily Bruner" holly begin stunted and curled (rule out
aphids). As the leaves grow, multiple holes with black, brittle margins appear.
The holes are elongate and rounded and are parallel to the venation. The leaves
with one or two holes may grow to full size, but those with multiple holes
remain comparatively small and misshaped. The tree is otherwise healthy, with
abundant new growth.

Answer
Donald,

It sounds like the holly has holly leaf miner. Treat the plant with a systemic insecticide to control some of the larvae this year, fertilize it in the fall and treat again for the leaf miner early next year (when the new growth starts to open),

Good luck,
Ed Gulliksen