I have not done a thorough study but this is a note a bit longer than a tweet. I will come back to longer posts sometime soon, together with more in the blog about Fleet Street and Europe.
I found out that Corbyn was in Brussels last week from a tweet linked to the Daily Express. I don't think there was anything in the print Guardian. Search through the Guardian found nothing online. Search through Google found this blog post with not much reporting if anything.
The week before he asked some questions of the PM about Europe that were fairly strong I thought. Again not much reporting, detail to follow.
So my guess is that although Corbyn is leader of the opposition the Guardian has not much intention of reporting what he has to say. The weekend before that the Observer editorial demanded he do more on Europe. So you might think they would report what he said and did.
So situation continues as in the referendum period. Corbyn is making a case but is just not reported, especially by the "soft" end of Fleet Street.