I want to find all cohort studies on type 2 diabetes published in the last 5 years. I used the following query:

"diabetes mellitus, type 2"[MeSH Terms] AND "cohort studies"[MeSH Terms] AND ("2010/03/09"[PDat] : "2015/03/07"[PDat])

However, among the results, there are some studies that don't have the "cohort studies"[MeSH Terms], but

• Cross-Sectional Studies[MeSH Terms]
• Longitudinal Studies[MeSH Terms]: Cohort studies are longitudinal studies which also include other study designs such as case control.

My questions are:

1. Why does PubMed return studies that don't have one of the query terms?
2. How do MeSH terms exactly work?
3. What is the best search query that retrieves only cohort studies on type 2 diabetes?

Thank you in advance for you help!