According to a Nature article from 1998 this is true (or at least, was in 1998).
Coelacanths were known for decades, but only as fossils. They appeared in the fossil record around 370 million years ago, had their heyday in terms of species diversity around 220 million years ago, and went into a long sunset that appeared to end with extinction, around 70 million years ago - just before the dinosaurs themselves perished.
And from later on in the article:
And why the huge geological gap - 70 million years - during which coelacanths must have existed, but are conspicuous by their absence?
The article goes on to suggest a possible explanation for the absence of fossils.
One answer could lie in the choosiness of the modern species, Latimeria chalumnae. Judging from its distribution within the Comoros, the fish prefers water that is both deep and cool - around 180 metres and less than 18 °C. In addition, it prefers to live near steep, submarine slopes pocked by caves. The Sulawesi coelacanths seem to prefer the same sort of habitat. But such pickiness is not extreme: there are probably many suitable places in the Indo-Pacific region that might yet harbour coelacanths.
Another answer is that the fossils of deep-sea fish of any kind, not just coelacanths, are scarce in the geological record. Historically, coelacanths occupied a variety of ecological niches, but deep-sea coelacanths are unlikely to have been preserved at all.
I.e. coelacanth fossils come from eras where they were widespread and occupied a large variety of ecological niches, whereas at their decline 70 million years ago they were left as a much rarer species that lives ina small number of deep ocean areas, and deep ocean species just don't leave many discoverable fossils.