69 Topps set questions

[DanP]

I just started putting together a 69 Topps high grade (PSA 8 or better) set. I have 313 cards so far. I have some questions for the experts out there:

1. What's the deal with the yellow and white letter cards? Was this done intentionally by Topps? Obviously the white letters appear to be a lot tougher to find, especially in high grade. I'm thinking of just getting EX or better for the white letters and focusing on them last.

2. I haven't examined the PSA POP reports yet but it seems like there are some commons tough to find in PSA 8 or better (i.e. #52 Mike Andrews). Any information you may have on the tough commons would be appreciated.

3. Card #99 Back loop/No black loop. Is this an error card? Are there other cards like this?

Do any of you have a checklist in a spreadsheet I can have?

I appreciate any insight or advice from the experts out there.

Thanks