You’re nitpicking, aren’t you? Linux kernel usually doesn’t just “invent” otherwise non-existing CPU cores. So if at some certain point linux kernel in ROS v7 showed 2 CPU cores, this pretty much testifies that SoC includes two CPU cores. Why propaganda materials from different vendors doesn’t mention it? Could be that also linux kernel, used by other vendors (many do, you know?), doesn’t support multiple cores. Could be that other vendors found out about problems earlier and already implemented workaround (of disabling second core). Could be that other vendors actually enable both cores but their UI doesn’t go into trouble of showing that. Could be anything else.
Sadly Marvell seems to hide spec sheets for their SoCs from general public so we can’t verify.