Most of the time, "HP" stands for "High Pitch." High Pitch is an intonation standard where concert A=457hz. Low Pitch, where A=440hz, is the standard that's in use today. Woodwinds cannot compensate for this pitch difference without having the instrument rebuilt.
This doesn't mean that the instrument is worthless. If you play unaccompanied solo, or accompanied by a sampler or synthesizer tuned to the right pitch, or with a string ensemble willing to tune to A=457, you're OK.
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post some pics.