Not surprising to me at all. The leaves of garlic are very different from onions. Thick, flat, and tougher than the thin, tubular onion leaves. Less water content too I believe.

Garlic leaves won't withstand the -6F we got here last week without mulch though. Luckily I planted mine late this year and there was only about 1" above the soil on a few of them.

Right, in cold-winter climates, garlic is generally planted in autumn and mulched, but onions are planted out in spring. Even if onions survive the frost, they might have vernalized and want to bolt asap.

I've only had young wispy Dixondale starts get exposed to temps around 20F here in March. Never larger maturing onions.

I imagine Dan's onions won't bulb up as well as they will need to put more energy into regrowing leaves and won't get back to the optimal 10-13 leaves by the time they start to bulb in late February.

Thanks. Onions are wholly winter vegetables here. 1015 sweet onions, developed in Texas, are named for their planting date. You plant them out in November. I have no experience with garlic, but the climate here (maybe, possibly, a light freeze in the winter) is one that makes us totally unconcerned about their cold tolerance. Very hard freezes such as this one are a blessed rarity.

Yes, about bulbing up, I was afraid of that. To the extent onion leaves correspond to onions layers, if you lose leaves, it stands to reason that you lose layers. We'll see. Now, around here, onions don't finish bulbing until May, and probably only start in April. You can pretty much set your calendar on harvest time. I'm planning on doing regular nitrogen fertilization this year for the first time. So maybe that will compensate. In any case, my 1015 bulbs are usually pretty enormous.

It's nothing to worry about Dan. Vernalization of onions can happen when they are actively growing in the vegetative or bulbing stage, or dormant and in storage, but other conditions must be met to change a onion's season to flower.
Onions must pass a juvenile phase before they are receptive to chilling and is dependent on the cultivar which ranges from 4 to 14 leaves. They also require temperatures below 50 degrees over a period of 60 days for complete Vernalization, and again depend on cultivar. All these numbers are for long day onions but the same requirements stand for short day cultivars to force them to bolt and flower in the same year, but actual values will be different and I don't know what they are.
Just like day light which is cumulative to cause bulbing, the same holds true for time required in the chilling process to cause total vernalization. A few days of very cold temperatures will kill the plants before it will change their season and yours didn't die so all is good. As far as leaf lose, there are some who think cutting half the leaves from the plants 1/2 way through the vegetative stage will give them bigger onions but I don't agree and anyone who listened to the nonsense and tried claimed it was not true. They believe it because they're parents told them this and a myth handed down generations. You will lose size but not enough to be worried about at this early stage of growth.

That's an interesting point about vernalization. Some onion varieties can be vernalized if the sets are chilled before planting. I'm asking Dixondale for advice, but two years ago, when we had another terrible freeze, I managed to keep the 1015s sort of healthy, and by summer, almost none of them tried to flower. They evidently didn't get vernalized. I'd like to believe I will also avoid vernalization this year.

Dixondale reports back that if the 1015 onions had 6-7 leaves before the freeze, and they all died, which they did, the onions will likely be smaller, and may well bolt. As in, they may have been vernalized. They're looking pretty good now but, oh well, I'll hope for the best. Now, that being said, my garlic was sure vernalized, and that's necessary!