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I think if authors were using some specific feed-models - connectors/cables - they would include at least corresponding note in the article.
The difference you observe is caused more probably by calcualtion settings, meshing or somethign like this. With including more details you should get closer to measurement results (describe more resonances), but anyway it is quite difficult to simulate exacty measurements performed by another people - there might be many uncertainties in real antenna, when you can not touch it yourself it is very difficult to reach exact match.