There is no missing text or cutscenes, in the original Contra there is almost zero text and custcenes exept the "game over" title.
You seem to be mentioning the scenes added to the Japanese release, which was made after the US release. Those are also not present in the original arcade game. They were never meant to be there, they were just added for the Japanese FC version and only that version.
Where did you get this info from? The Famicom version took advantage of the technology of Konami's VRC2 chip. The only reason for the cut content in the overseas versions is because Nintendo's NES licensing program only allowed North America and Europe distribution to include first-party hardware in its cartridges. Konami handled the manufacturing of their own games in Japan. Similar downgrades had to be made for Salamander/Life Force
and Akumajou Densetsu/Castlevania III
. And Gradius II
was simply not released outside Japan. All of these games used different custom made ships by Konami.
The original Arcade game and Famicom/NES game is two different beasts, it wasn't just a simple conversion. They were made by two different teams. Don't know how detailed the plot/objective was for the Japanese Arcade version but while Red Falcon is the name of the terrorist organization in the Arcade and Famicom Contra, the NES localization made it the name of the alien leader.
Plot summary of the FC and NES versions:
In the year 2631, a meteor crash-lands in the Galuga Archipelago. Two years later, the area is seized by a terrorist organization named Red Falcon that seeks world domination. 2 soldiers, Bill Rizer and Lance Bean, are deployed to neutralize the terrorist threat. During the mission, it is revealed that the enemy is harboring alien entities, likely originating from the meteor. The soldiers eventually stop the terrorists and eliminate the aliens.EDIT: Was looking into the Japanese manual backstory and my posted summary of it is wrong. It's clear right from the start that the Red Falcon organization are alien invaders, there's not even an attempt by either the manual or game to make that a surprise. Thank you, incorrect wiki article.
Rather than in the future, the game takes place in then-present-day 1987, where an alien race, led by an entity termed Red Falcon, has infested a Mayan village and is planning universal domination. These aliens likely originated from what was presumed to be regular space debris that crashed near the region 30 years prior. 2 soldiers, Bill “Mad Dog” and Lance “Scorpion” are sent to destroy the alien threat. Eventually, the aliens are destroyed, resulting in the entire universe being saved.
Also set in 2633, the plot of Probotector sees a future where science thrives. Top secret scientists discover that a malicious alien entity, Red Falcon, has set up a fortress in the fictional Galga Islands and intends to extinguish the human race. Sent to eliminate the aliens are 2 specialized robots, RD008 and RCO11 (replacing Bill and Lance). The robots ultimately stop the alien threat, saving the entire universe (same as the North American release).