Oliver, I quote from Michael Marissen's article on the Brandenburg Concertos in the Oxford Bach Companion (ed. Boyd, 1999). He has this to say about No 2:-

"It is often reported that Penzel's copies (a score and a set of performing parts) represent an early version with the horn in place of the trumpet... . Careful study of Penzel's manuscripts reveals, however, that ... the indication 'ô vero Corne da Caccia' was added afterwards to what originally read only 'Tromba', presumably because no trumpeters were available who could negotiate the part or who owned the odd size of trumpet required to match the ensemble."

Penzel was one of Bach's last pupils and is remembered as one of the most reliable copyists of Bach's works.

I think that's almost certainly the principle reason why valved brass instruments came about at the time they did, RB    When we were discussing "trumpets versus cornets" (in relation to the Rossini/Verdi repertoire and HIP) some while ago, Ollie pointed to a social division which limited trumpets (for various military and heraldic reasons) to the retinue of nobles, princes, counts, field-marshalls, margraves, landgraves, Electors Of Palatine, and sundry nobs and toffs.  No-one else could have them,  although they could play "on loan" elsewhere by prior agreement.  This "closed shop" gave little encouragement for technical development of the instrument, whereas the emerging prosperous merchant and professional classes in the C19th could afford to have cornets - and did so.  Once cornets had "pinched all the work" by dint of valves which permitted them to play conventional melodies in the "central" part of the treble clef , the trumpeters were forced to back-down and add valves likewise.   So this could be another reason why valves came late to the trumpet?

However, admirers of tradition and ritual will be pleased to note that trumpeters still consider themselves a race apart from other orchestral players,  reserving the right to send deps/their students/a sick-note to all rehearsals except the last two...  and when they do turn-up, they retain the right to adorn themselves in the finery of their Guild Livery  (a leather jacket, obligatory moustache etc).  A First Trumpet will refuse to "count rests" on demarcation grounds, thinking himself too important for such tedium - and depute this task to the 2nd Trumpet, who is obliged to do it for his boss

In my misspelt youth as a wannabe brass-player I had the huge privilege of meeting Christopher Monk - a man who knew more about playing, restoring and reviving historic brass than anyone else at the time (only CM could form a serious ensemble called "The London Serpent Trio" - of three serpents - the original line-up was CM, Andrew Van Der Beek and Alan Lumsden).  He had somehow acquired and restored a valved keyedtrumpet to playing order, and let me have a play on it.  The immediate problem I noted was the massive disparity of tone-quality between "closed" notes (where all the keys were shut) and "open" ones where 2-3 were open together, which made any kind of "legato" sound very ropey.  I think modern players of this instrument mostly go for a technique where you try "never" to use the "closed" notes (despite the rewarding sonorous timbre they have) and play entirely on "open" ones to produce a more even, if slightly strangulated tone across the range.  (It's also the instrument for the Hummel Concerto, the Hummel "Military" Septet, and quite a few other works).

Do you mean a keyed trumpet? I'm confused.

Having a moustache does indeed protect the lip from one particular hazard: shaving!

I'm a mere clarinettist but I do avoid shaving on concert days, at least if there's something strenuous to be played. I vaguely remember Barry Tuckwell advocating facial hair (a moustache and an 'imperial' in his case) precisely because of the need to keep blades and various chemicals away from the lips...

Well, do YOU want him anywhere near your lips?