Ok. So yes, the core book only has the Orcs and Humans. But all the other teams are available from the website. [https://www.bloodbowl.com/] Specifically, you are looking for the Teams of Legend down at the bottom (it should be noted that they changed the rosters a bit, mostly just names but a few bigger changes so make sure to look at your favorites, the coolest is that the Treeman on Halfling teams now have a special skill that let's 'flings help them stand up). Having said that, they are releasing Death Zone season supplements that add a lot of stuff. Stuff you may not want and/or need. I'll try to summarize the changes between the most recent Competition Rules Pack (aka CRP) and the new GW published edition...
The first change is the scale of the game. The old school board and figures were 28mm. The new board and figures are 32mm. However, dimensions of the board (in squares) remains the same. So you can play with the old board and/or minis. Range rulers won't work between editions but range tables/charts will. The general BB community seems to like this change. It's lets us play with slightly bigger minis so that means more detail and more viability.
An additional change people like is that the 4 minute turn limit and the Illegal Procedure rules are now officially marked as optional. Most people ignored them anyway, so.... good change. Humans catchers got reduced to 60k. There was a lot of fraccas about Pile On as a skill. Essentially, after errata, Pile On now places your player prone and allows you to use a team RR to reroll the Armor roll. Some people like this as it means Pile On now has more of a cost and cannot be used every single turn. Others, notably players who LIKE CLAW-PO-MB, are not fans.
Yes, Special Play cards are back. You get at least one a game, maybe more depending on the handicap. Two decks in the starting box but two additional decks have also been released. They are fun but I know some people don't like the extra randomness. Also, Wizards are officially gone (they will come back with Death Zone stuff). As in previous editions of the game, the core rules are intended for one of games, so you have to wait for Death Zone 1 to get league rules.
Additions in Death Zone 1: Seven races got published in new rules (Skaven, Dwarf, Nurgle, Dark Elf, Wood Elf, High Elf, and Elvin Union). More stars got added to the core four in the basic box (some are updated old stars, but some are new). MVP is now randomly assigned to one of three players you get to select. Minor tweaks to how you argue the call on fouls and secret weapons (basically, you now risk your head coach if you do this and that can have a minor negative effect later in the game). Spiraling Expenses is not optional but a new Aging rule comes into play between seasons in a league environment.
Additions in Death Zone 2: More stars (new and updated old). New optional league rules for marketing sponsorship and team owned stadiums. General consensus is these rules are rough. They contain some cool ideas but are not really balanced... yet. The community is working on alternatives that are more streamlined and fair. DZ2 adds famous referees and famous coaching staff who have special abilities. These are pretty cool ideas but again, don't look fully playtested.
And that's where we stand. Rumors are that Death Zone 3 will be undead focused. But no confirmation. Speculation on tournament rules as well.
As always, questions welcomed. I am all on board with Blood Bowl so I'll be buying whatever they release. [I know. I'm part of the problem.
] But it also means I can answer any questions you have.