How come this Lemmy community only shows the last 15 posts / 10 months worth of posts on Piefed?

This community or this community (from the same Lemmy instance) too are clipped, but they both show a year's worth.

Does it have something to do with the date at which the first PieFed user join them?

I know Lemmy instances only start mirroring a community hosted on another instance when someone on that instance joins it. But after that someone joined and the instance is done mirroring the community, the whole of it is browseable.

If I had to guess, I'd say Piefed instances only mirror the 15 last posts after the first user joins, or a years's worth, whichever applies. Correct?

And if so, does this also apply to native Piefed communities? In other words, does Piefied "disappear" older posts in Piefed communities?