Yes, the build number appears to be meaningless.
My system report shows the Security Update 2019-003 installed and I have the same Build number.
If the Security Update hung, it did NOT install. The last steps of the installation are very important including registering and activating the new components etc.
The main reason it hung is simple. Security Update tries to update your Recovery Partition with the latest Recovery Partition software and fails. You will need to update the Recovery Partition manually or delete it altogether first.
If you want to install the Security Update, you have three options:
OPTION 1. Backup your data and reinstall High Sierra on your unsupported Mac using Doddude1's installer BUT FIRST you will need to update Dosdude's installer with the last Recovery Partition software copied over from Security Update 2019-003.
(To do this, please see my post
https://forums.macrumors.com/threads/how-to-update-the-recovery-partition-in-high-sierra.2181484/ )
Option 2. Update the Recovery Partition on your Mac with the latest Recovery Partition software from Security Update 2019-003. After that is done, you can install Security Update 2019-003. (If you no longer see it listed in the App Store, you may need to download it from Apple'e website, hack it as described in the first post of this Thread and then run it).
If you want to know hoe to update the Recovery Partition, please see my post:
https://forums.macrumors.com/threads/how-to-update-the-recovery-partition-in-high-sierra.2181484/
Option 3. Delete your Recovery Partition from your Mac. If it is not there, Security Update 2019-003 will not try to update it. As a result, Security Update 2019-003 should complete its installation successfully.
Good Luck.