Question regarding arenas and seatings

[Arphaxad]

If I upgrade my arena to level 2 (3000 sitting places) and build an additional 1500 seatings, do I have a total of 3000+1500=4500 places?

What if I upgrade the arena to level 3 after the first level 2 upgrade, do the extra seating places disappear or do I still have those 1500 in addition to the upgraded arena? For example, if a level 3 arena has 4000 sitting places, will I have 4000+1500=5500 seatings?

The reason I'm asking is because when I look at my club info, it says that my arena has 1000 capacity. But when I look at the match report from my last game it says that the attendance was 800/800. There's 200 places missing in the match report. Is it because the 200 were extra seats built in addition to the upgraded arena? And why can't I fill those places during a game? I'm confused.