Longevity is the hardest quality to demonstrate in a portfolio, because it only becomes visible after the work has stopped being new.
Design the empty and the overflowing state
The mockup with three perfect cards is the least likely state your interface will be in. Design zero, one and forty.
Systems that handle their extremes gracefully absorb new features without redesign.
Name the patterns, not the pages
A documented pattern library survives staff changes. A folder of page comps does not.
The goal is that someone new can add a screen that looks like it belonged from the start.