Cave Story's website.

https://www.cavestory.org/downloads/dou_1005.lzh

 

Has there ever been any record for versions earlier than 1.0.0.5?

 

This was the changelog for 1.0.0.5:

Spoiler

* Reduced the CPU load.
* Expanded the 'Troubleshooting' section of the manual.
* Fixed the display of Naoku's picture in the manual.
* Added a sound effect for the Gravekeeper's attack.
* Added an effect for the Behemoth's charge.
* Fixed a bug in the Main Artery stage.
* Fixed a problem regarding processing issues on the title screen only."

I see