Ago and Before: The letter had been written four months before/ago

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hi

Could you please give me a few examples where “ago” and “before” can be used interchangeably? Are they interchangeable here?

Many thanks,

Tom

2

Hi Tom,
Here is a useful thread for you:

english-test.net/forum/ftopic24193.html