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I am not with Laminar Research; just a flight simmer.
My understanding is that once a new version is released there are no more updates available for the older version. This is also confirmed at the following link https://xplane.ultracartstore.com/checkout/singleLoad.do?r=1518566077769&merchantId=MEYER related to the purchase of version 9.
In my case the last update for XP10 was version 10.51 which ceased when XP11.0 was released having originally started with XP10.25
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