A development team has fine-tuned a language model to perform a single task: summarizing news articles. They created a high-quality dataset where every example was paired with the exact same instruction: 'Write a one-paragraph summary of the following article.' The model performs exceptionally well on this specific prompt. However, when beta testers use slightly different phrasing like 'Summarize this for me' or 'What are the main points of this text?', the model's performance drops significantly, often generating irrelevant or poorly structured responses. Based on this scenario, identify the most likely cause of this performance gap and propose a specific change to the fine-tuning dataset to resolve it.