You are welcome to answer questions posted in the Ask a Teacher forum as long as your suggestions, help, and advice reflect a good understanding of the English language. If you are not a teacher, you will need to state that clearly at the top of your post. Please note, all posts are moderated by our in-house language experts, so make sure your suggestions, help, and advice house the kind of information an international language teacher would offer. If not, and your posts do not contribute to the topic in a positive way, they will be subject to deletion.
Hello,
The following model "could+perfect Infinitive" refers the action to the past.
If you say "It could have been done in the long run",you mean that it wasn't done in the end.
E.G. I could have gone with you if had enough of time (I had an opportunity to go but i didn't use it, because i was lacking time)
Hello,
The following model "could+perfect Infinitive" refers the action to the past.
If you say "It could have been done in the long run",you mean that it wasn't done in the end - but that it would have been if you had not stopped when you did.
E.G. I could have gone with you if had enough of timeI had had enough time(I had an opportunity to go but i didn't use it, because i was lacking time)
Could have been 
Linear Mode
