nieuwguyski

Wow. The inner legs on that tuning slide are short! Your trumpet truly appears to be an odd duck, and I hesitate to claim that any typical generalizations apply to it, however:

Bb/A trumpets and cornets frequently don't have separate sets of valve slides for both keys. Instead, the valve slides are pushed all the way in for Bb, and pulled out to a scribed line for A. In this scenario, your trumpet wouldn't be missing any slides -- it would simply be a high-pitch Bb instrument with a tuning slide extension for A, and the valve slides would each have a line showing how far to pull them for tuning to A. Your finding the trumpet in this configuration would have simply been "all slides present and accounted for."

All I can suggest is try lubing the crook slide heavily with a thick grease to get a good seal without the extension slide and see how the trumpet tunes in its shorter configuration.

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John N. Nieuwguyski