I know NES games will, but I think SNES game will as well, when they read the button inputs, mirror them to RAM.
Look for the code the reads the addresses (again, making sure it is not confused with an actual memory address like 7E/7F:4218) and see if the results are being copied to somewhere in RAM.
It is very likely the data will be sent to RAM, so it can be further processed, such as filtering into "held" and "pressed" button state. (for the later, most humans probably cannot physically press and release a button at a 60hz rate, so input filtering, that is removing button inputs that are the same between consecutive frames, would need to be done so that a button registered as pressed will count as a single press, until the button is released, rather than count as 10, 20, etc. presses)
So you probably want to find that RAM mirror of the button data and check for that instead.
One example of this state I can think of is on the NES: pausing in Winter Games. It would seem like when Start is pressed to pause the game, the game is just ignoring Start inputs for some number of frames which it assumes is long enough for a person to lift their finger, and if it still is pressed after that, it assumes another press.
(that is, try pressing and holding the Start button to pause the game and keep holding for like a second or two, and notice it unpauses once the button is lifted.)
Then try a good game like Super Mario Bros., again press Start to pause and keep the button held for an exaggerated length. Lift the button and notice the game is still paused.