There are few issues here with your Rewrite Rules:
1) For Short URL redirects you are matching string such as /en-gb or /en-gb/ That is why your local redirects are working but not when string is "getstarted"
<rule name="Short URL redirects">
<match url="^/?[a-z][a-z](-[a-z][a-z])?/?$"/>
Should be <match url="(.*)"
or if you prefer reg ex as url="^/.*/?"
this will match /getstarted or /getstarted/.
2) In your rewritemap you need to specify key as /getstarted instead of just getstarted.
<rewriteMap name="ShortURLs">
<add key="getstarted" value="/en-us/get-started/"/>
Should be:
<rewriteMap name="ShortURLs">
<add key="/getstarted" value="/en-us/get-started/"/>