I think the issue with all models after 2012 was the lack of being able to replace the parts since everything was soldered on -- I could be wrong about the year though.
I know that on the 2015 rMPB the SSD is replaceable. You can even get a recent Samsung SSD and install it (provided you have the right adapter)
I ended up doing this last year. I bought a Sintech adapter and a Toshiba XG4 SSD for my 2015 15” rMBP. It works just fine but the battery life ended up being terrible compared to the stock SSD. I was getting around 60% of the battery life of the stock SSD with the XG4 + adapter combo.