Awesome! I love when those lightbulb moments happen.

Way to go, way to hang in there. It's always tough to feel like you're clueless - to go from really having a handle on your job & knowledge base to being the new kid & not knowing up from down.
For what it's worth, I love prorating! Hopefully this might help ...
I always had to prorate final checks for salaried employees. If they get $1,442.31 per two-week period and their last day is the first Wednesday of the pay period which runs Sunday through the following Saturday ... let's assume green means worked and red means terminated.
S - M - T - W - T - F - S
S - M - T - W - T - F - SIn this case, there are two different ways to prorate, depending on company policy. Some companies would say that weekends don't count for proration because they're not part of "regular business hours." Let's start there.
In the example, the employee worked 3 of the 10 regular business days. 3 / 10 = 30% and 30% of $1,442.31 is $432.69 of final pay to the employee.
In the other option, where the company says that weekends do count because more often than not salaried employees do work on weekends, the employee would have been employed for 4 of the 14 days in the pay period. 4 / 14 = 28.57% and 28.57% of $1,442.31 is $412.07 of final prorated pay to the employee.
The "downside" of this type of example is that it's the payout kind rather than the credit kind. So let's try another type of example.
Your pharmacist gives you 30 pills and charges you $10 (as if!).
Let's say that 15 pills in the bottle are crushed when you open the bottle. You'd expect to get $5 back since you didn't really get the full 30 pills.
In a bit more convoluted scenario, let's say you open the bottle and there are only 7 pills that haven't been crushed beyond use. That means lost out on 23 pills, right? If 30 pills cost $10.00, the cost per pill is $10.00 / 30 pills = $0.33. The pharmacist "owes" you for the pills you can't use or in other words, he will give you a refund of $0.33 each and that means you'd get $7.66 back. In other words, the pharmacist would pro-rate you for the unusable pills.
So in a service setting, if I'm paying $37.95 per month for a service but the service goes out of service for a chunk of time - let's say 6 days in a 31 day month. 6 / 31 = 19% of the whole. $37.95 x 19% (or 0.19) = prorated credit of $7.21 for downtime.
Does that help?