Rich Compared to When?

A culture in this world isn't a rank on a ladder from primitive to advanced. It's roughly nine separate dials, set independently, that can and do disagree with each other: a people can be exceptional metalworkers with crude ceramics, or fiercely stratified with almost no decorative tradition at all. And every one of those dials keeps moving, on its own schedule, without ever announcing when.

Nine dials, not a level

The attributes a culture is built from include things like trade openness, urbanisation, how sharply status is stratified, militarisation, religious emphasis, craft specialisation, decorative emphasis, how complex their motifs get and how conservative their forms stay across generations. None of these move together. A culture can score high on trade and low on stratification, or the reverse. There's no single number that tells you how "developed" a culture is, because that isn't a coherent question to ask of it.

It moves, and nobody tells you when

Those dials shift as a culture passes through its own phases, and every culture keeps its own phases on its own schedule, as covered elsewhere. No marker in the world announces "this is where the boundary falls." A culture that grew steadily more elaborate over three generations doesn't come with a sign reading "elaboration begins here." You infer the boundary from the evidence, or you don't, and if you get it wrong, you've just misjudged exactly the kind of thing the whole game expects you to misjudge.

Rich compared to when?

What counts as unusually lavish for a given phase is judged against the phase immediately before it, never against the culture's average across its whole history. That distinction matters more than it sounds like it should. A culture that gets steadily richer, phase after phase, would read as perfectly ordinary in every single one of those phases if it were being measured against its own lifetime average, because every phase would just look like "more of the same trend." Measuring each phase against the one before it is what makes a genuine change in fortune visible as a change, rather than smoothing it into an unremarkable long-run pattern.

Two cultures, many relationships

Relationships between cultures aren't fixed labels either. They're windows in time. Two peoples can trade heavily in one era and raid each other in the next, and in some periods, do a version of both at once, low-level hostility running alongside active exchange. Finding an object from Culture A made of a material sourced from Culture B doesn't hand you a clean conclusion. It could mean sustained trade. It could mean a single raid, decades before or after the trading window either of them would recognise as normal. You don't get told which era of the relationship produced the object in front of you.