Years ago I bought a Conn Concert Grand 36A cornet because of the weird construction (a Reynolds design) and because of the date of manufactering, serial number 3766xx, so I presume Februari or March 1948. And my birthday is 14th of February 1948 so I could not leave this horn behind.
This is the horn:

Conn 36A Photo by trumpetdelano | Photobucket

But I didn't blow the horn for years. Though some people with knowledge call it "probably the best cornet ever made" I could do nothing with it.
Only with a Wick 3 no letter I got a beautiful, very dark sound out of it which even could beat the flugel. But I could not play the Wick 3, too big.
And these horns are extremely mouthpiece sensitive. I had Jim New make me a Conn short shank backbore for Warburton thread but could not find the right cup. Later I ordered by Mark Curry a 8.5 BBC CSS mp but even this one did not fit the bill. The sound was still dull with a very bad low register and bad response.
So I decided to sell this cornet, made an advertisement for the German site Vioworld and ... forgot.
In the mean time I went on trumpet to bigger mouthpieces, first a Yamaha 14B4GP (and with Warburton from 6M to 4M) and later I bought an Arturo cup (Warburton), a TW's impression of Arturo's famous MtV 3C, (and I went from bb 7 to 5).
This is the best thing I did for my playing in six years, really an eye-opener, great combination with my Selmer trumpets (Concept TT and B700 tb). Big beautiful sound, great flexibility and great lows. And better endurance.
Last week my carry-on study cornet (Ambassador) fell of the table and I brought it to my dentfixguru, but I like to play cornet at home and on the road and then I remembered the 36A being still there.
Could find the Kanstul made bb in my drawer, did put the Arturo cup on it: end of all trouble. Sound, range, intonation, flexibility, attacks, high- and low register, everything top. Great, unbelievable cornet.
I did not play my trumpets since out of pure joy.
So the lesson is: don't sell an instrument, which is not great on first sight, too soon, there are too many variables and you need (a lot of) time to learn and to discover.