The codes aren't necessary. I skipped them altogether. You can use the save state function at every turn you experience difficulty.

There's no luck in beating any of these games, just heavy memorization. Every enemy that spawns in the screen is always a static spawn so long as you continue to keep the same pace and not idle too long in the same spot.

Most bosses all follow some sort of pattern and it's usually fairly static like 98% of the time. If any boss does have a random move set the tells are pretty easy to figure out once you've experienced them once already... not to mention, save states help with this issue. So if you have trouble in a certain spot, just save, try it... if you fail, reload and do it right the 2nd time.

The Konami Code only works on Contra 1... they changed the code for Super C, in fact there's three of them, one for 10 extra lives, one for a stage select and one for a sound test... I think the stage select code was removed in the NA release though and only works in the EU / JP release.

Contra NES: Up, Up, Down, Down, Left, Right, Left Right, B (Shoot), A (Jump) Start = 30 Lives

Super C: RIGHT, LEFT, DOWN, UP, A (Jump), B (Shoot), START = 10 Lives
Super C: Hold A+B and press START - Sound Test

Probotector II: On the title screen, press RIGHT, LEFT, DOWN, UP, A, B, START = 30 Lives

Super C JP: At the title screen, press RIGHT, LEFT, DOWN, UP, A & B = 30 Lives
Super C JP: At the title screen, press and HOLD DOWN and press START, then immediately hold SELECT = Stage Select

Contra III (JP ONLY CODES)

30 Lives (Japanese Version)
At the title screen do a hadoken style motion that is Down, Down+Right, Right and press start. You should hear the player dying sound effect if done correctly. You should position your cursor before entering it or you will start a 2 player game. You can position it above options and when you enter the options menu it will say Player Lives 30. The code remains enabled unless you change how many lives you start with in the options.
If you do you must re-enter the code.

Sound Test (Japanese version only)
At the title screen, quickly press: Right, Right-Down, Right and X. If done correctly you'll access the sound test.

Stage Select (Japanese version only)
At the title screen, quickly press: Down, Down-Left, Left, Up-Left, Up and Start for a 1-players stage select. Down, Down-Left, Left and Start for a 2-players stage select.
If done correctly you should see the stage select screen.

Contra Hardcorps (JP VERSION ONLY)

At the main menu, using controller 2, press C, B, A, RIGHT, LEFT, C, B, A, RIGHT, LEFT, C, B, A, RIGHT, LEFT. A confirmatory voice clip will be played = 70 lives

On the main menu, press LEFT, RIGHT, LEFT, RIGHT, A, B, C, B, A, UP, DOWN on the SECOND controller. = Debug Mode

Anytime during play, pause the game and press (on controller 1) UP, UP, DOWN, DOWN, A, Up, Up, DOWN, DOWN, B, Up, Up, DOWN, DOWN, C. = Gain All Weapons

At the main menu, using controller 2, press LEFT, RIGHT, A, B, C, LEFT, RIGHT, A, B, C, LEFT, RIGHT, A, B, C. A confirmatory voice clip will be played. = Level Select Menu

Operation C:

Up (x4), Down (x4), Left (x4), and Start = Extra 9 Lives (US/EU only)

Up, Down, Left, Right, Start = Sound Test (all versions) + 1 extra life (JP)

Up, Up, Down, Down, Left, Right, Left, Right, B, A, B, A, and Start = Stage Select (US/EU) or Extra 9 Lives (JP)