I completed my 1999 Lancair IV-P kit in 2008 and am reasonably sure there was
no SB or other instruction to add chicken plates in this area posted during that period. The fuselage is well rounded in that area, removing one of the principal reasons for installing them—to prevent peel-type separation of components where the pressure vessel
had square (as opposed to curving) joints. My IV-P has about 900 flight hours without chicken plates in this location, and I’ve had no difficulties with cracking/peeling in this area (or any other for that matter).
My opinion is that this is an example of an “improvement” that is not. At the minimum this adds unnecessary weight, and although I don’t
see it, could add stress on adjacent components. I believe that design work of the original engineers can occasionally be improved, but that this should always be undertaken with the presumption that there are always unintended, and sometimes unexpected, consequences.
My recommendation would be to remove the aforementioned chicken plates and patch the holes…
Bob