Whereas with third party material, it depends on whether or not another person knows about said material. Not everyone who knows about Level Up collects or has read its' 3pp material. So, I can now see where
@W'rkncacnter is coming from.
However, having first person content such as the core books doesn't always mean a person is going to remember a particular fact such as the Tyrannized culture providing resistance as well. When you brought up how you can get a resistance from your heritage and another resistance from your culture, I made a Knowledge check and remembered the Desert Hierarch culture from MoAR: Complete. It didn't occur to me to look elsewhere after that.

Nor did I know that I was going to start a discussion about first-party content vs. third-party content.

For Level Up, I consider the works of
@Steampunkette,
@PJ Coffey and
@Timespike to be just as good as first-party content.

They did work to help produce Level Up after all, and their work does appear in the Gate Pass Gazette.