In the case of Boeing, the last 2 numbers are the customer code and it indicates the airline that placed the original order for that particular aircraft. This number does not change and follows the aircraft even after it is sold. Cathay Pacific’s Boeing customer code is 67, so that explains the 777-367 designation. So for example if Cathay Pacific bought a 777-300 from American Airlines, and American had bought that aircraft directly from Boeing…it would be a 777-323 after Cathay acquired it, because that “23” is American’s Boeing customer code.

Regardless of the customer code, it is still referred to in the industry as a 777-300.

Newer Boeing planes like the 777X, 787, 747-8, 737 MAX series do not use the customer code system on their designation. This article may help.

https://en.m.wikipedia.org/wiki/List_of_Boeing_customer_codes

As for Airbus, I believe the number behind the series represents the engine option installed for that aircraft, i’m not 100% sure however.

Not sure where a list of all variations would be, but there may be something out there. Lots of companies can have similar subtypes, as fins change airlines frequently, be it by lease or sale. I flew the 767 for 4 years, and my company flight summary has about 6 different 767-300 variations broken down. We got our fins from all over the place, we had fins from Hawaiian to Ethiopian.