Singles that weren't included on Smash and the likely reasons for their exclusion

In many cases that would be "Singles" in quotation marks. Although their 2023 boxed set Smash has often been described (with some good reason) as a comprehensive and definitive collection of all of the Pet Shop Boys' singles up to that point, it excludes a quite a few PSB songs that might also—at least to varying degrees—be considered singles. Neil and Chris have been upfront about this and have, in a few cases, specifically stated why they weren't included. So here's a list of all such songs along with the likely reasons for their exclusion. Please note that alternate versions of songs that were nevertheless included, such as the original single version of "West End Girls" produced by Bobby 'O' Orlando, aren't listed. On the other hand, "singles" that were included in video format on Blu-ray discs with the five-disc edition of Smash but not on its CDs do qualify for this list.