A couple of points made during the thread worth mentioning. First, even
if the part number is the same, technically the part has no traceable
history evidenced by paperwork. Hence, installing it in an airplane
without paperwork/pedigree may render the airplane unairworthy. One
person noted that the Part 43 regs did not specifically mention that the
landing light bulb needed to be an "airplane" part. I believe if an
action was brought against you for this, you would lose. Other sections
mention proper workmanship/methods and I believe the finding would be
that approved parts are sufficiently implied.

Others cite "cases" where the basis of the finding was that the
unapproved part caused the airplane to be unairworthy, and thus a claim
was denied. Read the whole sentence. The parts were not approved for
that particular model AND there was a history of unacceptable
maintenance. Perhaps alone the parts would not have been researched.
Perhaps the other shortcomings in maintenance caused the closer
scrutiny. It is dangerous to draw conclusions from summary evidence
snippets.

Finally, as a practical matter, go through the logbooks of a 30 year old
airplane and inspect the beast to find ALL the discrepancies. It takes
loads of time and you need more than just a basic knowledge of not only
airplanes, but that particular make/model to make heads or tails of
these records. Harder still, what if no logbook entry was made? How can
you tell if the installed xxxx light bulb was recently replaced from the
Napa shelf, or was the one in there from Chief aircraft purchased a year
ago (for which there is an invoice or work order produced)? I doubt that
insurance companies have the time and/or talent (or will fund outside
"experts") to pour through the average spamcan books looking for
anomalies like this to base an "unairworthy" claim on.

HOWEVER, if there is an obvious aspect of the plane or crash that
attracts scrutiny and may negate their liability, I don't doubt for a
minute they won't look into it. Also true, the bigger the number, the
greater the incentive to take a closer look.

I believe the "airplane part and pedigree" is like a weather report. You
look it over carefully (the part, the pedigree, the weather) and make
your call as to what YOU believe is the truth (and what is safe). In
both the weather and parts quality it may be dangerous to blindly accept
what your are told and equally dangerous to outright reject it.

Good Luck,
Mike