The numbers are different because the package insert rates are based on two clinical trials while the information on Drugs.com is determined by Cerner Multum, a commercial drug database.

Adverse events frequencies reported in the drug prescribing information is typically determined by initial clinical trial data. The table included in your question indicates two studies as the source of these rates.

However, the very prescribing information you linked notes:

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Turning to Drugs.com, editorial policy page says:

The information available on the Drugs.com website is displayed under a number of licensing agreements with various publishers. For our drug-database information, we rely on the solid reputation of our suppliers: Cerner Multum, Micromedex and American Society of Health-System Pharmacists.

Indeed at the bottom of the Drugs.com zoledronic acid (Reclast) page we find:

References relevant to chosen section (Show all references)

1. Cerner Multum, Inc. "UK Summary of Product Characteristics."

If we review the informational page about Multum on Drugs.com

Multum's content is written by full-time associates who have no affiliations with drug companies, using a combination of sources. Initial References include the Product Information/Package Insert, primary literature and information from standards groups such as the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and the American Academy of Pediatrics.

Physicians and pharmacists review the new information and make any necessary changes; all leaflets are reviewed by one or more practicing clinical specialists. Content is verified using secondary references that include standard authoritative medical textbooks and the Multum Expert Review Panel.

Cerner itself is the second largest vendor of electronic health record technology in the United States, and so it is also possible that adverse events may be supplemented by information gained by their customers.

The numbers are different because the package insert rates are based on two clinical trials while the information on Drugs.com is determined by Cerner Multum, a commercial drug database.

Adverse events frequencies reported in the drug prescribing information is typically determined by initial clinical trial data. The table included in your question indicates two studies as the source of these rates.

However, the very prescribing information you linked notes:

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Turning to Drugs.com, editorial policy page says:

The information available on the Drugs.com website is displayed under a number of licensing agreements with various publishers. For our drug-database information, we rely on the solid reputation of our suppliers: Cerner Multum, Micromedex and American Society of Health-System Pharmacists.

Indeed at the bottom of the Drugs.com zoledronic acid (Reclast) page we find:

References relevant to chosen section (Show all references)

1. Cerner Multum, Inc. "UK Summary of Product Characteristics."

If we review the informational page about Multum on Drugs.com

Multum's content is written by full-time associates who have no affiliations with drug companies, using a combination of sources. Initial References include the Product Information/Package Insert, primary literature and information from standards groups such as the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and the American Academy of Pediatrics.

Physicians and pharmacists review the new information and make any necessary changes; all leaflets are reviewed by one or more practicing clinical specialists. Content is verified using secondary references that include standard authoritative medical textbooks and the Multum Expert Review Panel.

Cerner itself is the second largest vendor of electronic health record technology in the United States, and so it is also possible that adverse events may be supplemented by information gained by their customers.

Which source should be considered more reliable is difficult to say and probably opinion based.