Hallo barrin87
you wrote :
" I usually practice the most recent couple of pieces I'm learning 2-3+ times, then practice scales, and then spend the last bit going back to previous books to play a few pieces to make sure I can still play them. "

Certainly it is important to play pieces all over and play them several times.....
but when pieces get more and more difficult then it is very important to pick out difficult details and play them very slowly to achieve perfect intonation and nice sound
or make your fingers work perfectly and make them play the difficult detail quicker and quicker....
I like it very much to work on little details.

Best wishes to you from