In simplified terms any FM receiver, including scanners, will track any RF energy that appears within its defined bandwidth window and AFC settings. The frequency change value of a tracked carrier's center frequency is what sends both analog voice and digital data.
There is always a pucker-factor built in; if the transmitter's carrier center frequency is off (within limits) it will still work, If the center moves outside the receiver's defined window the receiver will consider it adjacent-channel interference and ignore it. If the 2.5KHz or 1.25KHz total frequency shift span of the carrier stays anywhere in a 15 or 6 KHz defined window, it doesn't matter if it is left, right or in the middle. All receivers do that differently, and some are better than others. Scanners are generally more forgiving than land mobile radios, and most were originally designed for a big, fat 5 KHz wide carrier wideband shift in a 20 KHz window.
The hard reality is that no receiver or transmitter has any idea what a channel's center frequency is, only where the tech sets it in relation to a (hopefully accurate) arbitrary and external analog standard. That's why there is a wide pucker-factor. The same goes for the distance the transmitted carrier shifts from relative center to send a signal. The radio's frequency reference can be anything from an old-fashioned crystal in most radios to an external GPS for base transmitters. Poking numbers into a keypad is all relative to the radio's aligned reference point, and bad alignment can send that off 0.05 MHz or more.
Errors, weakening signal strength and RF noise spikes will all cause poor audio. In analog that shows up as static which worsens starting the second you begin to move away from the source and continues until you exceed the receiver's front end ability to track a carrier relative to the background noise. The user's ear usually gives up first, and old ears seem to be better at it than young ones. Digital converts the analog carrier's frequency shift-stop-shift-stop into 0's and 1's, then a codec program extracts and simulates the voice. Data and voice information are sent at the same time, occupying different parts of the digital sentence's string of 0's and 1's. Audio quality and data work exactly the same over distance, up to the point the receiver has more noise than signal and abruptly stops doing anything.
In analog, the further the wandering offset the louder the voice, which is why wide-band scanners will still receive narrow band analog, albeit at a lower volume. In digital, the offset points are defined as distance from perceived center, and AFC with error correction can gloss over a lot. (Yes, digital is really sent via an analog carrier that shift-stop-shift-stops at predefined offset points for a defined period of time vs. the less defined wandering analog carrier that directly emulates the audio waveform.)
In the real world, no transmitter ever made by anyone is exactly on frequency, either as they age, as internal heat from transmitting changes the values of the components or as the frequency gets further from the aligned VXO lock point. Its all a shade of gray and generally transparent to a scanner's front end.
Is that why Motorola Allows all 5 or 6 digits past the . as in 769.206250. That might be one reason Motorola radios work better.
Vertex, Icom and others also do 6 decimals. Kenwood allows 5 or 6 decimal places depending on the model. No matter who made it the radio will reject any frequency data entry that does not fit into its defined channel spacing mask. Radio software allows a multi-decimal input for human interfacing, but many write a hex channel slot number instead of the frequency when it clones the radio.
As far as 'better' I have aligned M products that were at best scratchy at the 'industry standard' 0.25mV signal input. Many other brands will be full quieted at 0.25 and open with a usable signal at 0.18mV, and remain within 10 Hz after two minutes in transmit. The old GM300's are notorious for talking a long time to shift to the right frequency when first put into transmit, and for drifting south the longer they stayed in transmit. Even today M gave up tracking or sending the 1.25 KHz carrier shift (6.25 KHz super-narrow) that others do with their low end models, hence M's push to 2.5 Mhz shift TDMA and P25 Phase II (12.5 KHZ narrowband). 'Better' is a highly subjective perception.
But I digress; that's for land mobile radios and the radios that scanners listen to.
