Hello,

An AppLife update performs the actions that you specify when you build the update. Using AppLife Update, each individual update is self-contained, signed, and validated before being applied on the client.  Also, each update performs the actions that you specify, in order to update from one or more previous versions, to the current update version.  Replacing files is just one of many actions that an update can perform.  AppLife Update does not automatically synchronize client files with server files, an update performs specifically defined actions necessary to migrate a deployed client from version to version.

Expanding this on your example, you have two customers with different versions.  Customer 1 is running version 1.0, Customer 2 is running version 2.0. 

Note:

(If you had published an update from version 1.0 to 2.0, Customer 1 should be able to update to version 2.0 at this point).

Now you have released version 3.0 and want to publish an update.  Updating from version 1.0 to 3.0 requires replacing two files, and from 2.0 to 3.0 only requires replacing 1 file.  You can choose to target version 1.0 and version 2.0 with this update, or you can choose to just target version 2.0.  This would be a smaller update, but Customer 1, who is running version 1.0 couldn't use this update because it only contains one of the two files it needs to update all the way to 3.0.  So Customer 1 would have to first apply the update to version 2.0, and then apply the update to version 3.0.

The choice is up to you, the update publisher.  There are two solution labs related to this topic on implementing an update process that will chain individual updates together.  Find them here.

Also, a recent blog post discusses this topic as well.