We've lost far fewer than that. If you're talking about intact nuclear weapons, not test articles, training rounds, or weapons without a core, all of which count as nuclear incidents, but aren't lost weapons. A weapon has to be complete to work, so a lost training round isn't the same thing.
Airplanes have crashed with a nuclear weapon, but the weapon was recovered. That's not a loss.
The number of lost US weapons is very few. They were lost when the airplane (or sub) carrying them crashed (or sank).
In 1956, a B-47 crashed over the Mediterranean. The crew, airplane, and weapon were never recovered.
In 1957, a cargo plane jettisoned two nuclear weapons over the Atlantic. They were never recovered.
In 1958, a B-47 jettisoned a nuclear weapon over the Atlantic following a mid air collision. The weapon was never recovered, though groups have claimed that they found it.
In 1959, a Navy Patrol plane was lost carrying a nuclear depth charge. It was not recovered.
In 1965, the Navy lost an A-4 Skyhawk, loaded with a nuclear weapon.
The submarine USS Scorpion was lost in 1968, while carrying two nuclear weapons. The sub was found at a depth of 10,000 feet, but neither the weapons nor the sub were recovered.
Eight total U.S. weapons lost and not recovered in six incidents. The location of the Thresher is known, so while not lost, they're unrecovered...
Now, the total of US weapons damaged, etc. is much higher, but we are talking lost. None lost in the last 47 years. If you add up all the crashes and incidents where the bomb was recovered, the total might be closer to 50. But the number lost is pretty low.
Now, the consensus on the precise number of Russian nukes that remain unaccounted for varies. Numbers in the hundreds have been claimed by Russian officials, and that number has been denied by other Russian officials. This all surfaced in the 90s, after the fall of the Soviet Union. The Russians claim that they didn't lose any, but that their records are "incomplete"... So, how would they know?
At the time, Vice President Al Gore was on the case...but his inquiry never turned up anything conclusive...not publicly. Big weapons weren't the issue...smaller, more compact weapons that the Russians had built, so called "suitcase bombs", were unaccounted for.
They remain unaccounted for.