Master gardener here. The USDA maps are not kept up to date on a yearly basis. Usually every 5-10 years at best. The climate is changing in some places faster than others like Florida primarily due to the Atlantic Ocean and Gulf of Mexico warming slightly.
I would not get too hung up on zone 9a vs 9b and things like that. You can very often grow things 1-2 zones below their range as long as decent care is taken to the tree or shrub. Basically if you take care of what you're growing, they will be resilient enough to handle a cold spell.
When they say something is labelled for zone 10a, it doesn't mean that it will die if grown in 9a for example, it's really just an optimal suggestion.
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