Chosen Solution

Just wondering if a 2018 display retrofitted onto a 2017 machine would work?

The 2016 & 2017 systems share the same part, and the 2018 & 2019 systems share the same part. Sadly Apple altered the things enough that using the wrong display for your system won’t work properly. If you where hoping for TrueTone function to work on your older system I’m sure it won’t. Stick with the correct display for your system. Here are the cheapest parts I would go with from TheBookYard in the UK MacBook Pro 15" Complete Display - Space Grey (16/17) P/N 661-08030MacBook Pro 15" Complete Display - Silver (16/17) P/N 661-08031 Vs MacBook Pro 15" Complete Display - Space Grey (18/19) P/N 661-10355MacBook Pro 15" Complete Display - Silver (18/19) P/N 661-10356