All TV episodes not showing up in grid view

I've got 20 seasons of Top Gear all converted and waiting to be added to iTunes. They exist on my external HD, so when I drag them in to iTunes I hold in Alt/Option, so they stay there.

If I drag in the folders for seasons 1 through 13, all episodes show up, and if I select the show in iTunes I see "tabs/buttons" for Season 1, Season 2, etc etc. Pic here: https://dl.dropboxusercontent.com/u/2213114/2013-08-23_18-05-00.jpg

However if I drag season 1 through 14 (or more), only season 1 shows up in iTunes grid view. However all episodes/season show up in List view, and all are available on my Apple TV.

If I drag just, say, season 14 through 20, they add fine. But if I then add 1 through 13, again only 1 season shows in Grid view.

In all cases the correct number of "New" episodes shows on the blue banner on the cover (i.e "99+").

Top Gear generally has about 6 to 10 episodes per season.

I have exactly the same problem with The Simpsons.

All my other shows added fine. Just The Simpsons and Top Gear had issues. I doubt it's a co-incidence those are the only 2 shows I have with hundreds of episodes and 20+ seasons each. It's almost as if iTunes has some kind of limit…

Running iTunes 11.0.5 and OS X 10.8.4.

Yes I do, they all have their metadata tagged perfectly. If I add them 1 season at a time, they show up in iTunes perfectly. It just seems that at some point, there are "too many" and iTunes stops showing them.

As I said, if I look at them in List view, or on the Apple TV, they are there, with correct tags, etc.

Thanks guys, solved the mystery! I think, after 15 seasons, there are too many to show at once, so if I click where it says "No Season" or "Season 1" or whatever, I get a drop down to select any of the other 20+ season!