Above 500 points?

Neither. Point spent to enter GAs of the game you've just won were refunded to you, you'll be back to 400 point limit after you spend those extra points.

Sometimes if you win 1 giveaway and you entered in a few other entries for that game, all of the other entries' points are given back to you.

Also if you entered a giveaway that was then subsequently deleted for one reason or another before it ended, you get your points back as well.

Likewise, you can remove yourself from giveaways (say you entered two giveaways that were 50 points each), then your points accumulated back to 400. You then removed yourself from the giveaways, your total would then go up to 500.

I often see my points in between 400-450, because there are plenty of days I don't use them, and with some refunds, they go up above the 400 limit.

Actually I think what happens with me is that I activate a few games on Steam, and then I come here to Sync my account, and there may be a couple of entries for those games, and they are automatically refunded because now I own the games.

That limit is still there, so if you use your points and go below 400, it will only accrue up to 400 and stop.

Your account receives 6 points every 15 minutes. The automatic points generation will only give you up to 400 points and then stops until you reduced your points below 400.

There is no points limit on your account, you just stop getting points added to your account automatically every 15 minutes once you hit 400. If you are removed from a giveaway for any reason or a giveaway is deleted, your points used to enter are returned. If you win a giveaway, you are immediately removed from all other giveaways for the same game and if you were entered in a lot of giveaways for that game, you might get a large number of points back. Let's say you win a game that costs 10 points to enter and you were entered in another 30 giveaways for the same game. You will be removed from those 30 giveaways and be returned 300 points. If you currently have 95 points on your account, you will now be at 395 and at the next 15 minute cycle will only receive 5 points instead of 6 because that will bring you up to 400 points and you will not receive anymore points until you drop below 400. If your account already had 350 points when you got the 300 point return, you will now have 650 points and will get no more till you drop below 400.

If you constantly use all your points entering a lot of giveaways and then remove yourself from all those giveaways at the same time, you can have a few thousand points on your account. You can get a bunch of points back if someone deletes a bunch of giveaways that you were entered in. People shouldn't be deleting many giveaways, but sometimes it happens.

Edit: Also, if you activate a game on your Steam account, steamgifts doesn't know that you own that game until you sync your account or it syncs automatically. If you activate a game (or many), the next time your account is synced you will be removed from all giveaways for those games and the points returned to you.

I believe this is the last official thread about the points system update. You can find other discussions about the changes to the points system over the years if you search cg's created discussions for the word "point", like this.

Also, from the FAQ:

How many points (P) can I receive?
You will stop receiving points once you reach the maximum of 400 points. At that time, you will need to spend your points on giveaways before receiving more. In the below situations you might exceed the maximum point value.