Are spring national qualifying times really fast?

When I was registering for spring nationals, I didn't have any recent short course times to draw from, so I used my summer long course national times and the USA Swimming conversion tool for my entries. I was really surprised to see that times that were in the top ten at Mission Viejo, even a fourth place in the 1500, barely made the qualifying time for Santa Clara. Another time that was top 10 last summer didn't even make the NQT for spring. I've never done spring nats......is it a much faster meet? It seems like it's a much smaller meet, so how can I place well in a bigger meet and not even qualify for the smaller? Maybe it's the conversion tool, but every other time I used it, it was spot on. I don't mean to sound whiny, I can still go swim Santa Clara so all is good. However I am intensely curious. Sent from my ASUS Transformer Pad TF300T using Tapatalk