Thanks for the info. Any idea as to its resale value?

Unfortunately these are neither rare, in demand, or go for much money. I'd expect around $250 to $300.

Elkhart (correct spelling) was Buescher's second line, or student to intermediate line of horns before the mid 1960's buyout of the company by Selmer USA. Yours is a 20A model, which has rather thin brass construction, so use care when handling it. These are based on the very early progenitor of the True Tone model, but not in the same league. The date of manufacture is around 1920/1921, which would be in keeping with your description of the period case and it's purple cotton velvet lining. These are nice sounding horns, with usable if not antiquated keywork, but not worth a lot monetarily alas.