Some indeed said they did, but when you call the doctor's office, they say you can't do it. The website does not cover the in-between cases, it only explains upfront as sending the form in the package.
I called IMM, they said it is possible to do a late upfront. They said they would send an email with instructions on how to attach the results, but the email never came.
I suppose the attachment of results to a case is made through the webform, filling application number and other data... They can't miss it.
I just wasn't willing to take the risk. I read mixed information: some say you can do it and it is good to do so, some say you can't, and I even read somewhere you should not do it, as it could delay your app by confusing the system.
So I decided to wait, after all... what are 2 months from the total of 18? It can't get any worse anyway!