Generative Credits - Balance Confusion

Yesterday, Nov. 30, I tried to do a generative fill. I created a 1024x1024 selection, typed a prompt and clicked 'GO'. This resulted in a message saying I did not have enough credits to complete the function and maybe I should upgrade my plan. As with most folks, I've been experimenting to try to understand how all these features work; maybe I've used all my credits. Maybe it will reset tomorrow.

So I open Creative Cloud today, Dec. 1, and find the link to see my credit balance. It tells me I have 240/250 credits and that it will reset on Dec. 11. 

I don't understand this:

a) Yesterday I had NO CREDITS (or "insufficient")

b) Today I have 240/250, having performed NO edits or Gen AI functions.

c) I'm informed it will reset on Dec. 11.

a+b kind of makes sense, but why am I "missing" 10 credits

a+c makes sense since I think my annual renewal date is the 11th of the month.

a+b+c makes no sense to me.

(I installed a PS update today, if that affects this in any way. )

Can someone help me to understand this?

Thanks,

Ray