Not being in your zone, I'm a-guessing that if the temps dropped below, say, 25, for more than one or two nights in a row (or days!), yeah, they didn't like the freeze. I'm in Zone 5, allegedly, and I cover mine when the temps drop below freezing and they stay covered until I'm sure temps will remain above 38-40 at night, steadily. We had a nice warm-up the end of March here, but I didn't buy into it and left the covers on. It's now been in the 20's every night for two weeks and counting. I'm sure there are buds under there, but they won't see sun until I'm seeing proper nighttime temps for another couple of weeks. Don't worry, they're not smothered; just some old bedsheets and straw. I take it off in layers to harden them to the sun--they're pretty thin-skinned. (Like the author, I guess...) You may see some adventitious buds further back on the branches or trunk that may break dormancy later; if so, prune back to just above them and give it a little TLC this year. Bugs can be hard to spot, look for holes in bark or funny bumps or nodules. Your local extension office or gardening school (Japanese maple club?) may be able to provide more specifics. Hope this helps.