I hold the record...

The reason it gained 20 lb on your gross weight is:
It didnt. The scales float, therefore even a wind or you moving around in/on the truck will create movement & could weigh different every time..
The company I work for recycles plastic. The industry buys & sells scrap & recycled plastic by the weight. To ensure (somewhat) accurate weight for the buyer & seller, we have to get both empty & full weights. I will sometimes get 2 or 3 empty weights at a time so I will have a spare empty weight on hand, so I dont have to go to the scales every time for empty weights.
There are times I can get 3 empty weights & all be different somehow. CAT scales weigh in 20 lb increments.

I'll take that advice & give you more. If you find yourself over axle a couple hundred pounds but not over gross, I could almost guarantee you wont be bothered at the scale houses.
Why?
A couple of reasons. One because of the above post, even wind can affect the weight. Being over a bit could be questioned by you or the scale master. Too many factors involved & its not an exact science.
Secondly, its just like speeding, they will always give you a little room to play with. If the police stopped everyone who was 5 mph over the limit, the shoulders would be packed with police writing tickets. If the scales brought everyone in who was 200 lb over axle, the scales would be packed with trucks getting tickets. There is leeway.
Dont burden yourself over 20 lbs or 200 lbs. Especially when you're under gross. Try to get legal, but its not always possible especially when the shipper tries to load you close to max... or when the wind is blowing etc.

I agree that 250 lb per hole is usually the norm.
I agree that some trailers have longer spacing between holes, (I think 6") & those are about 400 lb per hole I think.
I agree that moving the fifth wheel has no affect on trailer weight.
I agree that if you'r going to be over on an axle, make it the drive axles.

It hasn't been discussed but the way I figure how many holes to move is:

36240 - 31480 = 4760 (subtract your light axle from your heavy axle)
4760 divided by 2 = 2380 (because your equalizing/dividing the weight of 2 sets of axles)
2380 divided by 250 = 9.52 (because each hole is 250 lb)
I would have moved/slid the axles toward the back of the trailer 10 holes. Because you always move the axles toward the heaviest point. If you're heavy in the rear, move the axles to the rear. That moves the weight to the front. Why 10 holes instead of 9? Personally, I always like my extra weight on the drives as a rule. But as mentioned above, as you burn fuel, the extra weight comes off your drives.
In the above scenario, your steers were fine, no reason to move the steers (fifth wheel).
After I have moved the axles according to the above, I can re-weight & adjust if needed. You should be good on the second weight.... third at most.

Another important issue I learned after many headaches. DO NOT set your trailer brakes on the scales. There are a few threads here on why.

Hope this helps. Good luck........