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In Set(O) form under Tier 2 migrant section, what is "For the period before you were granted leave as a Tier 2 migrant, documents showing that you met the relevant requirements of the immigration rules"

Thank you for your help

I also noticed the same thing as am applying for ILR in Feb 2017.

My previous BRP's (when each time I renew Tier 2) are kept my the Home Office. What else to provide? Photocopies of the BRP? Previous Tier 2 CoS letter?