I don't agree...

The problem is you are leading folks down a slippery slope. There is
more to meeting the design intent of a certificated part than
conservative assumptions and good intentions. One thing I know from
parsing JAR-22 and older European design criteria is that they do
things differently, mainly safe life vs fail safe. They still have
this approach today, one modern glider requires ALL cables to be
replaced every 10 years.

Have you ever compared the countersink depth and angle from the "5"
rivet on the Blanik with a NAS1097 or
NASM20426? I did the layout, and they are not the same geometry. I
have never seen the proper factory rivets used in a Blanik repair, and
the folks doing the work are completely unaware of the nuances of
bearing properties of mismatched flush rivet in csk or dimpled
structure. They would not know the principle of bearing bypass if it
hit them upside the head.

If one does not have skills or experience, "designing" something based
on a single data point from a used, damaged old part does not meet the
intent of the FAR's or certification criteria, even if you do have a
tensile tester and know how to use it AND reduce the data to "B"
basis, ect.

You need the original design data and specs, and Blanik has extensive
overhaul, repair, and maintenance manuals. BTW, AC-43-13 cannot be
used if you can't ensure that the data therein is not contrary to the
Mfg data.

Lets encourage folks to support the Mfg and buy the right parts if
available. lf we all did that, perhaps they will stay in business and
the prices will come down.

aerodyne