Import an AVI file into Sony Vegas Pro 12

I will try to contribute to a recurring problem regarding the import of an .AVI video file into Sony Vegas software.

My presentation unfolds in three stages.
First stage (mid-May 2014)
Situation: I have .MOV files and others in .AVI telling mundane family stories. But I care about them.
I have three different software programs for editing: Cyberlink Power Director 12 and Sony Vegas Movie Studio HD 11 and the identical version 13.

With Cyberlink, everything works: both AVI and MOV, and I should be happy.
Since I like to dig deep, I also explore Sony software. One sometimes has commands that the other does not.
And then: catastrophe: the AVI file doesn't work. I wrote: no response.
On Sony, an AVI file is cataloged as unknown.
It's hard to believe, knowing that these two software programs are the top of amateur video editing.
Naturally, I used a converter (Movavi) that allowed me to transform the AVIs into MOVs, and of course, the Vegas Movie Studio recognize them and everything is back in order. I don't find this satisfactory, however, because it requires going through a conversion that inevitably, even if it's not visible, slightly destroys the original work.
So I have two or three questions:
1 - Are these compatibility issues common?
2 - Is Sony's inability specific to Sony?
3 - Is it advisable to use a converted MOV file for the final editing?

Second stage (24 hours later)
I found the solution by chance with Xeros on YouTube under the title: How to import an AVI file into Sony Vegas.
And all this after writing to the Americas without getting a response!

It's a Codec issue that can also disrupt audio editors like Audacity or Samplitude. But that's not today's topic.

In this case, here's what to do:
1 - Download the latest version of "K-lite-mega Codec pack."
2 - Start the installation of this executable.
3 - Once the installation is started, participate in the setup by checking EVERYTHING and especially not forgetting the audio, which is disabled by default. Otherwise, your videos will remain silent.
4 - Don’t panic, some pages may come up three times in front of you. That’s normal.

Second stage (mid-June 2014)
It's a complete failure. Cyberlink continues to do its job with any video file, while Sony no longer wants to import AVI format, citing: unknown format.

Description of the repair procedure for the failure.
I uninstall "K-lite-mega Codec pack" and reinstall the latest version that was updated in June 2014.
I make sure to carefully configure the new "K-lite-mega Codec pack" during installation (choice no. in the list of choices, destination: desktop, 3 vertical boxes to uncheck when the choice presents itself, checking all video and audio files when the choice appears).
Finally, turn off the computer and turn it back on in two distinct maneuvers and not by “restart.”
Then, do some PLAYBACK with VLC media player and then with QuickTime, and especially not with the "Windows Media Player" of Windows 7.
Only then can you open Sony Vegas.
Just before importing the problematic AVI file, the following question is asked by the two Sony Vegas software: "Do you want to set your project video settings according to this media?" Answer: NO.

That's it. And it works! ...

I spent 24 continuous hours to fix this failure.

Let’s remain humble ... because there may be other solutions that I do not know.
Given the complexity of the problem, I suggest that those involved in this subject take the time to detail their theories in terms understandable to all. Thank you.