I'm responding to these parts together. Samantha's boyfriend was the one who identified this as being the trail up to Vesper Peak. You can see this in the comments on the original video. He is familiar with the area, and is also the one who made the main map on the findsamsayers.com website. While I wouldn't put it out of the realm of possibility for him to have been mistaken, I don't think that it's likely.
Futhermore, the maps that are shown there are for laypeople as you mentioned, and were made by the boyfriend Kevin Dares and his family, who have a good amount of experience in the area, so it's not just random inexperienced people that are filling in the map. This is to encourage witnesses to come forward and to examine their footage. It was also intended to help people who wanted to search, but couldn't read the actual search and rescue maps. The maps below the one that gives the timeline are the maps that were released by the sheriff's department and the family as the search was ongoing.
There are more official maps out there on the findsamsayers facebook page that were given to the boyfriend after he met with them last week. There is also an official Sam Sayers rescue group (this is private, you have to ask to join), which is only for people who can assist in the actual search. The maps are posted there as well. Based on what I have seen of them, and overlaying them with the laypeople maps, they pretty much line up.
I finally had a moment to go back through some news articles, and the most recent of them do NOT place her at the summit at noon. Witnesses say she arrived at the summit at 3:00pm. Here are two such articles:
From August 27th, 2018:
Seattle woman still missing after not returning from hike nearly three weeks ago
From August 20th, 2018:
https://www.heraldnet.com/news/search-for-missing-hiker-nears-3-weeks-as-family-clings-to-hope/
Of note, in the NBC news article, they mentioned that the "lunch witness" saw her twice: once while eating lunch (supposedly around noon) and once while he was on the summit around 3:00 p.m. However, this article still contains the inaccuracy that he ate lunch with her (this isn't true as confirmed by the Sheriff's Department).
The Herald mentions: "A small rock climbing group bumped into her just before 3 p.m. at the summit. A man eating lunch at the top noticed Sayers, too. He did not eat with her, as the sheriff’s office had reported earlier, O’Keefe clarified Friday. That witness has been working with deputies to pinpoint her last known movement, possibly to the southeast."
The Herald is a more local newspaper, which tend to report better on these kinds of incidents, so I'm inclined to believe their version. However, in any recently published article, it is the 3:00pm summit that has been published.
I also had some time to look this up. The only thing I could find was on the family's page, which said they were able to "ping movement" on her phone. Here is the link to the Heavy article that mentions this
Samantha ‘Sam’ Sayers Missing: 5 Fast Facts You Need to Know | Heavy.com, since I don't know if posting a link is acceptable.
Phone pings can be fickle things as we've seen in many cases. If the only two pings they have are the ones that are on the maps they posted, I stand by that that likely does not represent movement. The towers are too close together for that to be movement. If they had say 7-8 of them all moving in one direction, then yes, that would look more like movement to me.
One interesting thing about this is that it isn't mentioned in any media reports after August 9th, whereas I think this is very important information. Still, it would suggest that Sam was not able to use her phone to call for help, as you pointed out. Her family mentioned the phone was in a white case, so it could have had some extra protection from the elements.
