Neither of these songs are technically 8-bit. What program do you use? For my 8-bit tunes, I use a program called
FamiTracker, which allows you to replicate all of the limits the NES originally had.
If you wish to use a different program, such as FL Studio, just remember that you can only have two square waves, one triangle wave, and one noise channel playing at a time. There are many instances in both tunes where more than two square waves were playing at a time, and thus the song is no longer 8-bit.