假设我有一个由不同句子组成的字符串。我期望删除以It was formerly known as开头的部分，直到这句话的结尾。我想停止清理，直到它达到. Withey Limited。如果不是这样，它结束清理，直到. It。

import re
txt = 'It was formerly known as A. Withey & Black Limited. Withey Limited delivers many things. It has a facility in the UK, including many branches.'
out = re.sub("\s*It was formerly known as [\w\d\s@_!#$%^&*()<>?/\|}{~:\.]+" + "(?=(. Withey Limited |. It))","", txt)

这段代码返回. It has a facility in the UK, including many branches.'，这不是我的预期结果。我的预期结果如下：

Withey Limited delivers many things. It has a facility in the UK, including many branches.

如何调整正则表达式以达到这个结果？为什么它会这样？