I haven't opened up Portal 1 ever to see whether a run's legit or not, I don't even really know if I intend to ever. Here's what I do know - if you're not willing to put in the effort to record your run as one continuous video, then please do everyone who needs to see your run a huge steamy solid:

There's a nifty command I saw Forest, css bhop legend himself, use to play a thread of demos in succession which encompassed a larger run of a big map. You would start by typing 'startdemos' and include a space between each demo name. For instance:

startdemos speedrun speedrun_2 speedrun_3 speedrun_4 speedrun_5 speedrun_6 speedrun_7 speedrun_8 speedrun_9 speedrun_10

So if you're going to upload demos, perhaps put this command somewhere in the comments as a courtesy to whoever is downloading your demos to verify your run. Thanks for reading