From Michael Swan: As is well known...

[Tom]

Hi

M. Swan suggests that it is not required in the given sentences:

1- They lost money, as (it) was expected.
2- The train may be late, as (it) happened yesterday.
3- As (it) is well known...
4- As (it) is in your knowledge that a new campus is...

I would like to know if it is wrong to put it here or there is also a difference of opinion somewhere! Secondly, he does not deal with this topic in detail. Look at the given sentence please.

1- The train may be late, as (it) was yesterday.

What about this one? Even it is wrong here?

Tom

[Yankee]

Hi Tom

In the first 3 Swan examples, adding the word it would sound very strange. I'd never even consider adding it.

The 4th Swan example sounds strange to me both with and without it.

In your example, omitting the word it would result in your sentence meaning that yesterday was late (rather than the train).

Amy

[Tom]

[Yankee]

[Tom]