Hi chevron,
Down our way it's the Senior Service, who may do things differently from their colleagues in pale blue.

Fortunately, they bandbox UHF and VHF controller transmissions, so we can guess when they're talking on UHF i.e. they say something and there's a deafening silence as far as we're concerned, then there's a further transmission. Usually, you can fill in the gaps yourself.

I used to hear 'stud' when getting a 'service' from Benson, so I guess it's a difference between the Services. Occasionally, they'll read out the full UHF frequency, mostly to visiting aircraft flying down from England.

TOO

Yes it's only home based aircraft who are given the 'Stud'; visitors will always get the full frequency.
When we used to do Odiham radar and director from Farnborough, we were Odiham's 'Stud 3' whilst Farnborough approach was ( I think) 'Stud 5' to an Odiham aircraft and 'Stud 2' to a Farnborough aircraft.

When 8.33 was first introduced the 8.33 frequencies were referred to as Channels but this seemed to cause even more confusion and was dropped.
In the marine world there is only a limited number of frequencies around 150 MHz so Channel numbering is convenient however; with 8.33Khz there are theoretically 2940 channels (760 + 2180)
In the main, the military use stud numbers for two purposes, frequencies were programmed to studs on some radios so no need to dial in frequencies, allowing more flexibility and to stop others following them to the next frequency.
Eurocontrol is still referring to channels
There is no ratio, all civil aeronautical communication is VHF. The Military use UHF but when aircraft are operating as civil air traffic they will be talking to civil ATC on VHF. There are military controllers embedded into the civil ATC system and military aircraft on operations may well be talking to RAF controllers on UHF. These controllers look after seperation with civil traffic. On V bombers we flew Navexes that took no account of civil airspace, the military controllers on the ground did all the work. I anticipate its much the same with our fighters today, we don't seem to have bombers any more.

Garmin is quite clear on it:

Thank you for contacting Garmin Support regarding the issues with your device. Unfortunately, GNS is not able to store 8.33 frequencies in the Navigation Database. I need to explain briefly some technical details regarding Navigation databases to help you understand the root cause of the problem. The original Navigation database format for the GNS series was designed in early 2000 ‘s when 8.33 frequencies were not being used in aviation, nor were there any plans to do so in future. This is why the format of the Navigation database does not allow to code 8.33 frequencies. This could only be achieved by designing new format of the Navigation Database. We call it ADB1 for the old format and ADB2 for the new format. ADB2 increases amount of information associated to each airfield which allows to code 8.33 frequencies as well as additional approaches and more. Sadly, GNS production has been discontinued years before the ADB2 format was created and therefore currently available and certified GNS firmware is not compatible with it. Garmin is monitoring the impact that this is having on our customers, but due to the discontinuation of this product and severity of the firmware changes required, it is unlikely that new software will be released to resolve the issue. Please accept our apologies for the inconvenience caused.

Some marine VHF channels are composed of a pair of frequencies to allow the use of repeaters located on high ground to extend range. Aircraft don't generally need to use repeaters. since you're supposed to already be above the highest ground most of the time!