请教SET-O条款请教

SET-O 第78页:
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.

请问,这个需要提供什么材料啊?

个人理解是提供t2之前的签证。不过之前的BRP卡都被收走了

当时也迷惑过,申请的时候这一栏啥也没写。
网上说是有关t4转t2的情况的,如果不属于就什么也不用填

明白了。谢谢