Because they aren't persistent (the objects that have received permissions from an ACL Template aren't aware of that ACL Template), updating an ACL Template does not affect any objects that might have previously received permissions from that ACL Template.
An ACL Push will only update the 'users' file on a target based on the permissions of the Server object - which is also separate from an ACL Template.
Therefore if you make updates to an ACL Template, you will need to re-update any objects that you would like to receive the permissions of that template.
On the other hand, ACL Policies are persistent. Objects with an ACL Policy will be updated automatically as soon as changes are saved to that ACL Policy.
Fantastic! Thanks for the help Greg. Long live the ACL Policy!!