As others have mentioned you won’t get 40X the points because of this; multipliers don’t stack.
So in the spreadsheet you’re comparing 20% off to 20X the points. Goes as follows:
$379 is the reg price.
$379(0.8)(1.13) = $303.2(1.13) = $342.62 = cost on 20% off day
You’ll get base points only so 15(303) = 4545 pts back.
On 20X days
$379(1.13) = $428.27 = cost on 20X day
20X the points so 15(20)(379) = 113700 pts back.
So even if you don’t use the points back to their maximum value you’re still getting a better deal on 20X the points day as long as you plan on using your points.
For example you could use the points you got back on a redemption day to get $140 worth of switch accessories and games for 100K pts