As some have already stated, don't make assumptions and go off exactly what YOU observed. Do not assume the server name on the receipt is correct, unless stated in the guidelines otherwise. Note that it's usually OK to have "Unknown" as their name, as long as you provide a description.
If you were served by multiple persons, I pick one way or the other; the cashier or the actual person who served me my food. In the report, I'd include my interactions with ALL crew members, with the name / description in my narrative, if possible. Since this is a Food Comparison Study, be sure to be as consistent with your approach as possible. If your case, I'd list one of these as the "server" in the report:
Option 1:
"Restaurant # 1 - One person took my order and took my payment."
"Restaurant # 2 - A person named Josh took my order."
Add into the narrative about your interaction with the expeditor, in addition to the above.
Option 2:
"Restaurant # 1 - Another person gave me my food."
"Restaurant # 2 - A woman with no name tag (that I could see) gave me my food."
Add into the narrative about your interaction with the ordertaker, in addition to the above.
Very infrequently shopping the Greater Denver Area, Colorado Springs and in-between in Colorado these days.