You say that "we rely on them for top 10 verification", this is in a very small part true. For the most part we rely on live videos for top 10 times. The only thing that demos actually help us verify for a top 10 run is whether a jump script is being used.

The rule is that you require both for a top 10 run, since having exclusively a video or demos is flawed in terms of conclusive proof that the run is legit.

for SPT in particular y_spt_pause is set to 1, so that can be checked, idk if demos save timestamps upon ending and starting recordings, but if you're games starts paused you have to also unpause it, another thing possible to track in the console.

really it'd be more trouble than it's worth. It is definitely possible, but it's a bitch to do. i'm also guessing the mods have some demo tools that they use to determine whether it's legit or not, similar to how HL1 is verified.