I'm still not sure yet what addons those are, but I doubt it would have been the editor update. I can't be certain on that, but I'm pretty sure. If you are using the editor update, then you would not have recieved any "missing addon" errors.
There are times that older missions, or newer missions at times, use addons that are rare and hard to find. In those cases, if you can't contact the original author of the mission to locate the needed addons, I think the easiest solution is what was told above. Find the addons in the mission.sqm, and replace them with a similar file that you do have. It's just a matter of renaming the addon, and then go into the editor to figure out what it was used for, so that you can replace it with something you have. In some cases you can just delete it completely without trouble, but it's best to check it first like we did with the tanks, and see if they were in a spot that looked important.
Thinking about it though, I think the theory that they were roads was correct. They might have been part of some STT road or texture pack, but I didn't see them in any of the STT files I found, including the island used. But "sttasfaltka" sounds like STT Asphalt maybe? Not sure, maybe someone should try and contact SelectThis and ask him about it.
So as of now, the mission works? Were you able to download the rest of the addons ok?