First Retina MacBook Pros 13" were with 8 GB base memory. That was either 2013 or even 2012, so, yeah.

You could (unsupported) run 16gb ram on 2010 rMBP models, back before it was soldered on. Worked great, not to mention swapping the spinning drive for an SSD.

At this point, I get the soldered on ram, for better or worse... I do wish at least storage was more approachable.