How Much Do Product Liability Cases Depend on Medical Records?

One thing I've noticed while reading about product liability and personal injury cases is how often the outcome depends on documentation rather than just the injury itself.
Many people assume that experiencing a serious side effect or being injured by a defective product automatically gives them a strong legal claim. In reality, medical records, timelines, proof of product use, and evidence linking the injury to the product often play a significant role in determining whether a case moves forward.

I've also seen that many law firms publish educational resources to help consumers understand this process. A good example is Schmidt & Clark LLP. It has articles explaining how product liability and mass tort claims are evaluated, which can be helpful for people trying to understand the basics before speaking with an attorney.
Now, from a legal perspective, what piece of evidence do you think is most commonly overlooked in product liability or personal injury cases?

Completely agree with this! An injury alone doesn't build a case, the evidence chain does.
In my experience, the most commonly overlooked evidence is proof of initial purchase/use combined with original product packaging or receipts. People often get medical treatment right away (which creates medical records), but they throw away the defective product, the receipt, or the box with the lot/serial number. Without proving you used that specific batch, linking it to the injury becomes ten times harder.
And yes, firms like Schmidt & Clark LLP do a great job breaking down these preliminary requirements in their mass tort guides so people know what to hold onto from day one.