Why does joomla write that the version is the latest, even though it is not?

Question

Joomla

Good day to all.
The crux of the matter is this. There is a web server for Debian 8. Njinx + Apache. Joomla content.
It has 2 sites on joomla. I didn't do how they are tied to each other, I don't understand, but there is a problem:
When I got to them, both sites were on version 3.4. There was a task to update both to the current version of Joomla.
I started by updating the first one - I updated it automatically through the admin panel. Everything is fine, the first site was updated to the intermediate version 3.6 without any problems.
I go to the admin panel of the second one to update to 3.6 as well and I see that there
"Jumla version is up-to-date. Joomla version is 3.4. Updates are not required"
It is worth adding that before updating the first site, updating Joomla on the secondwas available. I rolled back the system and tried to update the second site first. Then the problem with "update is not required" arose already on the first . I don’t understand how they are related to each other, because all their content is located in different directories.
Actually a question. How can I update my site if Joomla doesn't want to update itself? I'm afraid to update by replacing files, because something can be missed? and the site is down? How can you indicate somewhere that the update is still required and version 3.4 is not up to date?
Plz tell me what to do in this situation?

Answer 1

In order not to be afraid to update Joomla by replacing files, make a backup copy of the site files and database, and then go ahead, without fear of irrevocably ruining something. By the way, in any case, that when updating from under Joomla, that when rolling up an upgrade package - the same files are replaced, there is no difference.