I have not paid attention to leaf sizes but I do know that when leaf out is very late after new growth, new growth sometimes appears to play catch up growth-wise and gets close to 1/2 the size of the old wood. At that point, it makes me think that new growth might surpass the old wood until suddenly, errrr, the leaf out starts.... The leaves from the new wood are usually awake for several weeks (maybe 3 weeks? even 4 week?) before leaf out starts. That time would be long enough to completely unfurl the new growth leaf buds and start expanding the leaf dimensions by a lot.