I don't have a Toyota sat nav so I cant help you with the complexities, I see you made a post in the Garmin forum last month & thatNeil AKA Surethingdidn't respond. He doesn't visit so often now since it became against forum policy to post direct links to maps which may violate copy write.
Unfortunately the inbuilt sat nav's have turned from a dream to a ripoff.
As you have read the threads here you will know it's not as easy as most GPS to update at a reasonable price.
There are ways around it if you investigate some forums like & .
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