ETSI EN 300 220-1 868MHz frequency precision
These frequency bands are intended for OOK modulated signals, see: https://en.wikipedia.org/wiki/On-off_keying

Basically the RF signal is 100% AM modulated (on or off) in a certain sequence giving a certain code. This code is then used to identify which command is transmitted.

The OOK modulation does not mean that the used frequency space is more than 25 kHz, it is simply on or off at a frequency in that 25 kHz space.

Receivers for OOK signals are generally wideband (much wider than that 25 kHz), the actual separation of information (is this signal for me ?) is done on the transmitted code. So all codes are recived and a microcontroller checks if it matches any code the receiver needs to respond to.

This means that you do not need to worry about that 25 kHz spacing as long as you stay within the assigned frequency band.