E: Failed to fetch ... 404 Not Found \n E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Question

I am receiving

$ sudo apt-get install ffmpeg
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libavdevice57 libsdl2-2.0-0
Suggested packages:
  ffmpeg-doc
The following NEW packages will be installed:
  ffmpeg libavdevice57 libsdl2-2.0-0
0 upgraded, 3 newly installed, 0 to remove and 574 not upgraded.
Need to get 378 kB/2.040 kB of archives.
After this operation, 3.824 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Err:1 http://us.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 libsdl2-2.0-0 amd64 2.0.8+dfsg1-1ubuntu1.18.04.1
  404  Not Found [IP: 10.1.... 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/pool/universe/libs/libsdl2/libsdl2-2.0-0_2.0.8+dfsg1-1ubuntu1.18.04.1_amd64.deb  404  Not Found [IP: 10.1.... 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

If I browse http://us.archive.ubuntu.com/ubuntu/pool/universe/libs/libsdl2/ as the message says, there is no
libsdl2-2.0-0_2.0.8+dfsg1-1ubuntu1.18.04.1_amd64.deb.

There are, for instance, files
libsdl2-2.0-0_2.0.8+dfsg1-1ubuntu1.18.04.3_amd64.deb
libsdl2-2.0-0_2.0.8+dfsg1-1ubuntu1_amd64.deb

Actually, I do not see any file *18.04.1*. I see some *18.04.3*, *16.04.01* files, and others with no specific version.

So, Can I perform the intended sudo apt-get install ffmpeg without upgradeing?:

1. Can that file be located somewhere else? (and how to tell Ubuntu to use it).
   I googled like this. The first link does not have the file, either in the page displayed or in the source. From the second link, I managed to get libsdl2-2.0-0_2.0.8+dfsg1-1ubuntu1.18.04.1_amd64.deb.
2. Can that file be superseded by some other alternative? (and how to tell Ubuntu to do so... see ... upgrade below)

What I tried:

1. 
   $ sudo apt-get update
$ sudo apt-get install ffmpeg

2. 
   $ sudo apt-get install ffmpeg --fix-missing

3. 
   $ sudo apt-get clean
$ sudo apt-get update
$ sudo apt-get install ffmpeg

4. Replacing in /etc/apt/sources.list all the instances of us.archive, archive or security by old-releases, in lines http://<search string>.ubuntu.com/ubuntu/ ... (see https://stackoverflow.com/a/30843486/2707864). I got errors like

   $ sudo apt-get update
   Err:8 http://old-releases.ubuntu.com/ubuntu bionic Release
     404  Not Found [IP: 10.1.... 80]
   Err:9 http://old-releases.ubuntu.com/ubuntu bionic-updates Release
     404  Not Found [IP: 10.1.... 80]
   Err:10 http://old-releases.ubuntu.com/ubuntu bionic-backports Release
     404  Not Found [IP: 10.1.... 80]
   Err:11 http://old-releases.ubuntu.com/ubuntu bionic-security Release
     404  Not Found [IP: 10.1.... 80]
   Reading package lists... Done
   E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic Release' does not have a Release file.
   N: Updating from such a repository can't be done securely, and is therefore disabled by default.
   N: See apt-secure(8) manpage for repository creation and user configuration details.
   E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic-updates Release' does not have a Release file.
   N: Updating from such a repository can't be done securely, and is therefore disabled by default.
   N: See apt-secure(8) manpage for repository creation and user configuration details.
   ...
   

What I did not try:

$ sudo apt-get upgrade

I am not sure if I risk my system having issues which may take time to fix. If so, I would upgrade when I have some time available to deal with the potential contingency.