They’ve steadily expanded over the years, I wouldn’t be surprised if this was real. It’s not just calculators, TI chips show up in a lot of military hardware in particular.
The r&d isn't expensive because these are legacy/old type chips. There isn't much r&d happening. They're made using old processes.
Any r&d is likely using different materials. Military stuff often uses different materials for specific applications.
The profits come from raising yields, which is much easier on older nodes.
Given the low transistor count, you could probably achieve speeds in the multi-10s of GHz, it would be so small.
A multi-core 99/4A would be hilarious to witness.