SN74HCS04-Q1: What is the difference between SN74HCS04-Q1 and SN74HCS14-Q1?

The difference between '04 and '14 is that the latter has Schmitt-trigger inputs.

But in the HCS family, all devices have Schmitt-trigger inputs, so there is no difference at all. The two HCS04 and HCS14 part numbers exist as replacements for the corresponding HC devices.