你所说的连接副词其实就是疑问副词，你所说的缩合连接副词就是融合型关系副词。由于你使用的术语粗糙，混淆了疑问副词和融合型关系副词的本质区别：疑问副词引导的名词性疑问分句本身就是一个特殊疑问句，wh-词仍然有疑问含义。而融合型关系副词引导的是名词性关系分句，相当于一个被限制性定语从句修饰的名词词组。wh-词是关系词，没有疑问含义。例如：

I asked why he did it. why是疑问副词。why=for what reason。 不等于 the reason why。

This was why he did it, why是名词性关系副词，why = the reason why。

有的时候，wh-词引导的名词性从句可能有歧义，需要根据上下文判断其究竟是疑问分句还是名词性关系分句。

主句为被动语态时，名词性关系分句可以直接作主语；名词性疑问分句则必须外置，用it作形式主语：

Where he used to keep his collections has been changed into a public muzeum. （正确）

Where he used to keep his collections has often been asked by historians. (错误）

It has often been asked by historians where he used to keep his collections.（正确）