I recently began a new project with new coworkers. The project being huge, it involves 100+ people whom I have to talk to and work with on a regular basis. I don't know everyone and everyone's role yet. 95% of my coworkers are abroad and I never saw them, and 90% I didn't have to work with them yet.
My role is very broad and I guess that's why I find myself in charge of things I'm not supposed to take care of. For instance, there are some projects I ended up leading because the competent person is a contractor and not an employee of my company and they're not allowed to access the private documents we have to fill to make those projects succeed. That implies sending emails and scheduling meetings for somebody else. That somebody would then send me a list of people to invite or to send the emails to.
Two issues rose from this, the first one being that sometimes, some unknown coworkers would come to see me and ask me things about our project and they don't tell me who they are and what they want. This makes me afraid of being tested for social engineering and I look like a fool when I discover it's my boss's boss's boss who told them to come to me and they didn't tell me. The other issue is that sometimes I don't send the meetings invitations to all involved people at first because I've not been told to and I either have to send it at the last minute or there are some people missing at the meeting.
An example in which Coworker A asked me to organize a meeting and sent me the list of people to invite two weeks ago:
Coworker A: Regarding tomorrow's meeting, I talked about it with Unknown Coworker, they said that you have to do this to prepare it...
Me: So should I invite Unknown Coworker to the meeting?
In this situation I'd like to point out to Coworker A that they didn't tell me to invite Unknown Coworker in the first place but I'm afraid of being rude for pointing out a mistake. But the thing I'm most afraid of is being accused of not inviting the right people or inviting them last minute because I was warned to add them just a little bit before the meeting.
How can I indicate that I wasn't told to invite those people without sounding like accusing the coworker who asked me to plan the meetings?