Phrasing leaves some confusion alongside nid:1472317632103
Both cards use the phrase 'after birth' which is insufficiently specific and leads to a similarity between the two cards that leads to confusion and apparent contradiction.
Fusion to form the atrial septum happens during embryogenesis (in contrast to fusion to close the foramen ovale, which happens postnatally).
Source: FA, page 284 (2024 edition).
Osmosis: https://www.osmosis.org/answers/interatrial-septum
Wiki: https://en.wikipedia.org/wiki/Interatrial_septum
Your citation of FA24 pg 284 states that the "septum secundum and septum primum fuse during infancy/early childhood, forming the atrial septum."
