This is an excellent thread.
I am currently trying to put together a complete 51' Bowman set. Prior to taking on this task, I laughed at the idea that the high numbers were more challenging to find. I used to think this whole thing was a marketing ploy. However, it has been a few months now since I've been working on this set and I realize that I was dead wrong.
High numbers really are tough. Whenever somebody lists a group of these cards for sale online, there probably won't be a single high in there. I also think that the PSA Population Report gives us the wrong idea, because we don't see a big difference between the highs and lows, however, that's only because collectors are
more likely to submit a high in for grading.