I got Nolan's report in the mail. Most of the frequencies were fairly stable, though he lost a considerable amount of hearing at 4,000 Hz in the right ear. His hearing at 8,000Hz also dropped by 10dB in that ear (I'm less concerned about that frequency because it isn't really in the main speech frequencies).
Here is his latest audiogram:
He can't hear anything above the red and black lines (without hearing aids). This basically means he cannot hear any speech sounds without aids (this is the same situation as his last audiogram - kids who hit the moderately severe level are usually completely below the coveted "speech banana").
His speech discrimination (closed-set, WIPI) dropped from 100% at 80dB to 80% at 80dB. I managed to get aided discrimination at 50dB with the same WIPI cards and he scored 96% using both ears in a soundfield (while wearing hearing aids).
His bone conduction scores are showing less of a gap than they used to show - a 15dB gap between his better-hearing ear and the bone conduction values. His loss is predominantly sensorineural, though there is obviously some small conductive component at play. The bone conduction at 250Hz is generally disregarded because it is vibrotactile - kids feel rather than hear bone-conduction tones at this frequency.
His hearing has been slowly progressive. I put all of his audiograms together and made a short video out of them, to show the progression over time. There is a significant change from birth, but the progression is very slow.
You can see the amount of lost hearing (summary) in the audiogram below. The blue line is from his first behavioral test at the age of 8 months, and the red/black lines are from his test last week. The lost sounds are highlighted in pink - he has a very slowly progressive hearing loss, but the sounds he has lost are significant (they include ch/sh, r, and k).