That’s only mostly true.

One apparent exception is l’Hospital’s rule. Here is a relevant clip from l’Hospital’s Wikipedia entry:
“In 1694 he forged a deal with Johann Bernoulli. The deal was that L’Hôpital paid Bernoulli 300 Francs a year to tell him of his discoveries, which L’Hôpital described in his book. In 1704, after L’Hôpital’s death, Bernoulli revealed the deal to the world, claiming that many of the results in L’Hôpital’s book were due to him. In 1922 texts were found that give support for Bernoulli. The widespread story that L’Hôpital tried to get credit for inventing de L’Hôpital’s rule is false: he published his book anonymously, acknowleged Bernoulli’s help in the introduction, and never claimed to be responsible for the rule.”