[2] The first HP-12A (HP stands for high performance) was built by a series of amateur sailplane builders, each contributing to the construction.
It started off with Art Heabener of New Jersey constructing a rear fuselage from the plans for the original HP-12.
It was in Illinois that Hall sold the still-incomplete aircraft to Rudy Kunda and Bill Carlson in 1977.
Kunda indicated that he does not know why the Federal Aviation Administration identifies it as an HP-12A, but it is a 100% Schreder design.
[3] Data from Sailplane Directory and Soaring[1][2]General characteristics Performance