Each of us gains every year approximately .3 of an IQ point (6 IQ points every twenty years), and this has been found for nearly 30 nations. It was a secret before Flynn and others made this discovery because the IQ tests were periodically re-normed and the average scores were reset to 100 even if the average person had actually scored a 106. The size of the IQ gain is smaller on tests that are more directly taught in school and home (e.g., vocabulary, arithmetic) and largest on tests that would seem unrelated to schooling (e.g., matrices, detecting similarities).
I think the first sentence is wrong. I think of an IQ test as a test given to a cohort of people, meaning people of approximately the same age. The test places you in a percentile within the cohort. Within a cohort, it is impossible for "each of us" to gain. If my percentile goes up, then someone else's percentile has to go down.
When I think of the Flynn effect, I think of differences across cohorts. Suppose that I took at test at age ten, and the 50th percentile score was 27 out of 40. Thirty years later, another group of ten-year olds takes the same test, and the 50th percentile is now at 29 out of 40. So young folks are on average smarter than old folks were when they were young, but old folks are not gaining anything.