Lightroom 6.14 update no longer available
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I found a link that advises by logging in to your Adobe Account it is possible to download the latest version but it seems to be for those who downloaded the original from the site rather than those who purchased a DVD. My version is registered and is shown under the Product tab (without a version number allocated) but the only clickable area is to enter the serial number which it returns with ”An error appeared while registering” presumably because it is already registered. Other tabs for My Plans, Order history, and Billing history are not applicable to a DVD purchase.
So it looks like I am stuck with version 6.0 if Lightroom ever needs re-installing.