After AEM migration from 5.6.1 to 6.2 I realized that node /etc/tags was missing. After migration procedure step-by-step check it was found that it was 6.2.0 hotfix 12785 version 7 that removed /etc/tags node.
Is there any change in AEM 6.2 related to tag node location? Is this behavior expected? In our case original content was restored from production and everything seems to be fine.
After the upgrade, check if the tags were moved under "/var/upgrade/PreUpgradeBackup". I have seen this in the past. If tags are indeed moved there, you can move back the tags to etc.
During the upgrade AEM will attempt to backup customizations and store them beneath /var/upgrade/PreUpgradeBackup/<time-stamp-of-upgrade>. In order to view this folder in CRXDE Lite you may need to temporarily enable CRXDE Lite.
The folder with the time stamp should have a property named mergeStatus with a value of COMPLETED. The to-processfolder should be empty and the overwritten node indicates which nodes were overwritten during the upgrade. Content beneath the leftovers node indicate content that could not be safely merged during the upgrade. If your implementation is dependent on any of the children nodes (and not already installed by your upgraded code package) they will need to be merged manually.
I am not sure about moving from 5.6.1 to 6.2 but there has been repository restructure moving to 6.4 including the location of etc/tags  so the same may have happened in the older versions but I never worked with those versions so I am just giving you an idea that its entirely possible that the same thing has happened: