That changes the risks/rewards of early-patching quite a bit. They can be confident it's their own trump card for quite a while, and learn about (or strategically mislead) any teams that arrive later to the same knowledge. When it's really "burnt", and in use by the NSA's enemies, then they can help US companies patch... and possibly even assure them exactly how much damage (if any) occurred.
(In the extreme, with say a big friend-of-NSA telecom or defense contractor, that could even be: "Hi, American BigCo. In the 48 hours between the beginning of enemy exploitation and your patching, we saw about 13,000 suspicious heartbeats directed at your servers. If you don't have raw traffic logs to do your own audit of exactly what server memory was lost, we can share our copy with you. It's a pleasure doing business with you.")
In fact, perhaps the reason for the synchronized reveal from US and non-US discoverers just now is that the first non-NSA probing (by either malicious actors or researchers) was just recently detected, starting the race to patch.