Installing package with gdebi incorrectly finding newer version of package

Question

I am trying to install Emacs version 25.1. I have the .deb package for this, which I created using checkinstall. This was part of the short tutorial that I followed (perhaps the clue is there somewhere).
After installing, I could open version 25.1 from Terminal, simply typing emacs. After rebooting, the installations seems to be completely gone. Performing tree / | grep emacs-25 (and various alternatives) showed me that the only version 25 files are found in my ~/Downloads/ folder, containing the downloaded source code, i.e. there is nothing in '/usr/bin/` and the like. It seems no executable file was created.

But, not to worry... that tutorial provided me with the .deb package. I had a look for ways to use this local package, and plumped for the gdebi variant. Trying to execute this, I see this:

Or on the command-line:

user@user:~/Downloads/emacs-25.1$ sudo gdebi emacs_25.1-1_amd64.deb 
Reading package lists... Done
Building dependency tree        
Reading state information... Done
This package is uninstallable
A later version is already installed

So I looked at the meta-information of this package:

user@user:~/Downloads/emacs-25.1$ dpkg --info emacs_25.1-1_amd64.deb 

 new debian package, version 2.0.          <-- is this the problem?? -------
 size 41650584 bytes: control archive=355 bytes.
       0 bytes,     0 lines      conffiles            
     295 bytes,    10 lines      control              
 Package: emacs
 Priority: extra
 Section: checkinstall
 Installed-Size: 129208
 Maintainer: root@user
 Architecture: amd64
 Version: 25.1-1
 Provides: emacs
 Description: emacs25.1

Is the marked line really what is being taken into account, when comparing to the system's installed version 24?

Update: output of apt-cache policy emacs

test@test:~$ apt-cache policy emacs
emacs:
  Installed: 46.1
  Candidate: 46.1
  Version table:
 *** 46.1 500
        500 http://de.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        500 http://de.archive.ubuntu.com/ubuntu xenial/main i386 Packages
        100 /var/lib/dpkg/status

A quick search shows me that this might be a known occurrence. Any up-to-date fixes or methods to resolve this are welcome!