Two different things here, Vince.
A vehicle remains registered, until it is de-registered, or you cease/forget to pay the annual road tax. A vehicle can remain registered without being road-worthy, or having a valid testing sticker. Just not allowed to use it on public roads in this case. No vehicle can be registered without a valid test certificate.
Germany has a scheme allowing 30+ year old vehicles to be specially registered, with unlimited use. Isn't any cheaper, unless you drive some sort of gas-guzzler that would otherwise cost horrendous emmission-based road tax. Actually more expensive for smaller vehicles, as a blanket tax is applied to all these vehicles. Classic rego does require the vehicle to be basically standard, or carry contempory accessories only, at least outwardly. As long as contempory parts are used in the drive line, modern upgrades, within boundaries, are allowed.
Type-approval comes into the equation every 2 years at the mandatory T?V inspection. Due to the multitude of ultra-quick sports bikes, and a multitude of tyre offerings, bikes are often homologated with a specific brand and dimension of tyre. Other tyres can be added in the vehicle documents, but this necessitates an approval, either in the course of the bi-annual inspection, or a seperate inspection, both of which require statements from the vehicle and tyre manufacturer that the particular tyre is satisfactory for use on that particular vehicle. No problem for most brands of bikes, but owners of defunct brands are dependant on the experience and goodwill of the inspectors. There are a lot of arseholes amoungst them that are more than happy to play out their "power", but there are quite a few dedicated enthusiasts that will allow mods that they deem safe. Base requirement for inspectors is an engineering master degree, so most
should actually know what they're talking about.
So, it's not as gloomy as it seems.
piet