“This additional data will play a big role in this,” said Dr. Worobey.

It is not clear why this valuable information was lost in the first place. Scientists can request that files be deleted by sending an email to the managers of the Sequence Read Archive. The National Library of Medicine, which manages the archive, said the 13 sequences were removed last summer.

“These SARS-CoV-2 sequences were submitted for publication in SRA in March 2020 and then withdrawn by the filing investigator in June 2020,” said Renate Myles, a spokeswoman for the National Institutes of Health.

She said the investigator, whom she did not name, told archive managers that the sequences would be updated and placed in a different database. But dr. Bloom has searched every database he knows and has not yet found it. “Of course, I can’t rule out the sequences might be in another database or on a website somewhere, but I couldn’t find them in any of the obvious places I looked,” he said.

Three of the co-authors of the 2020 test study that produced the 13 sequences did not immediately respond to emails asking for Dr. Bloom’s findings were asked. This study did not include contact information for another co-author, Dr. Fu, who was also mentioned in the table of the other study.

Some scientists are skeptical that there was something sinister behind the removal of the sequences. “I don’t really see how this suggests a cover-up,” said Stephen Goldstein, a virologist at the University of Utah.

Dr. Goldstein noted that the test paper listed the individual mutations that the Wuhan researchers found in their tests. Although the full sequences are no longer in the archive, the key information has been public for over a year, he said. It was just hidden in a format difficult for researchers to find.

“We all missed this relatively obscure paper,” said Dr. Goldstein.

“You can’t really tell why they were removed,” confirmed Dr. Bloom in an interview. “It can be said that the practical consequence of removing them was that people didn’t realize they existed.” He also noted that the Chinese government ordered the destruction of a number of early samples of the virus and the publication of papers on it Coronavirus had banned without their approval.