Which source of information is the least reliable for moving and positioning a complex patient?

The option indicating communication with a bystander who witnessed the incident is considered the least reliable source of information for moving and positioning a complex patient. This is primarily because bystanders may lack training and expertise in medical scenarios, and their observations could be influenced by emotion, stress, or misunderstanding of the situation.

In contrast, clinical notes from a previous visit provide documented medical history and specific instructions, which can be crucial for making informed decisions regarding a patient's care. The patient's own verbal communication is vital, as it offers direct insight into their needs, comfort levels, and any pain they may be experiencing, which is essential for safe handling. Information from other healthcare professionals is typically based on their specialized training and experience, making it a reliable source of information regarding the patient’s condition and care requirements. This highlights the importance of using trained professionals and documented medical sources to guide safe manual handling practices.