Ron -thank you!  The card holder idea was one I saw online - just figured out a way that worked for me.  As my tops weren't thick enough to simply make a slot, I added walnut on top.  

Once I made the mistake with the cherry I had planned for the top, the other decisions to add in walnut came into play.  I tend to do some of my design "along the way" so it all worked out.  I too like the contrast between the cherry and walnut.  

I agree that some mistakes can be quickly addressed (like switching from the cherry to walnut top), but mis-steps near the end for me are typically more distressing and time consuming.  Part of that may be a finish line mentality where I let my focus slip, or the timing just allows less flexibility in recovery.  

Doing more test cuts is another good suggestion I need to implement.  Thanks for that note.