I used to have an older copy of ICAO aircraft designations -apparently the official manual on what to call planes, which also gave info one engine type and number of engines. When interpreting data from all over the world, we'd come across plane abbreviations that we just didn't recognise, so would use it regularly as our bible, and as non-engineers it stopped us having to guess the differences between turbo-prop and prop on small things.

We didn't notice, until the RR guy pointed it out in some data that we had sent him that 767s didn't have 4 engines, despite the ICAO guide saying they did! I was never quite sure though, if this was the official book listing designations, did that mean all 767s with 2 engines were wrong?!