This was my thought as well when reading this. In particular, travelers who've failed to register using TWOV or the Shenzhen visa have had issues on subsequent visits. I haven't read of issues for travelers with a prearranged visa. There was a previous data point on one of these threads within the last year of someone who tried but failed to register. The difference in that case is that there is at least documentation that the poster had tried (and was unsuccessful in) registering if the issue surfaces on future trips.