Thanks @miguelito – I got your media and took a look at this. I understand the issue, and it’s not entirely straightforward, so first a couple baselines points to understand:
Editing in Roon is a work in progress – right now you have a good deal of control over how your music is displayed, and for most fields you can choose to display the data Roon has retrieved from our metadata service, the information that’s in your tags, or any data you enter by hand in Roon.
What’s not editable right now are the links displayed in Roon – so if any album is tied to a performer (either as the albums main performer, or via a credit), that link cannot currently be edited (although we will be changing that at some point in the future).
The second point to understand is the difference between main performers and album artist, which is a little counter intuitive at first, but which is ultimately a very flexible and powerful way to credit the albums in your collection. Consider the case of groups like James Brown & the Famous Flames or The Miles Davis Quintet – these groups released albums, but are they distinct from James Brown or Miles Davis, respectively?
It’s really very subjective, but I think it’s fair to say whether or not you consider them full fledged “artists” in your collection, you probably want their albums to appear on both pages, meaning on the James Brown & the Famous Flames page, and the James Brown page. This is why you sometimes see two rows under an album’s name – one is the main performers of that album, and the other is the Album Artist, meaning whoever’s name was on the cover or spine.
So, to explain your issue, first keep in mind that AllMusic considers the name of the group to be Carpenters, not The Carpenters. Also note that, in a wacky twist, they consider the album artist to be The Carpenters. 
So, you can see below what shows up on the album’s page. Note that because The Carpenters don’t appear in any meaningful way in Roon’s database, it’s not an active link, as seen here:
Moving on, the home brew album has no match in Roon’s metadata of course, so the tags are used as is. As such, the album is credited to The Carpenters, whereas all the identified albums are instead credited to Carpenters. So, they aren’t grouped together under a single artist. Still with me? Incredible, if so 
So, what can you do? I would recommend changing the tags in your home brew album to Carpenters, then rescan the album, and watch it magically group in with the other albums. Once Roon considers these to all be Carpenters albums, you can even edit the display name for the group in Roon if you’d prefer to see it displayed with The.
Phew. Does that make sense?