Add a new xmatter pack named "traditional"

 This puts the credits page on the back of the title page, rather than the inside of the front cover. This is good in cases where you pay by the page imprint, rather than by pieces of paper. You can select it from Settings:Book Making:Front/Back Matter Pack. Once you have chosen this, you won't see it on any existing books until you do these steps: In the Collection Tab, click on the little triangle, then select "Advanced: Do Updates of All Books".
I'm surprised that you include this and NOT the new Traditional-XMatter.css.

Also, if you deliberately include the original, I'm surprised that there are so many rules in the new one, since it seems like all you're doing is inserting a typically blank page and moving the credits page to a new place, so additional/changed styles should be very few.