From time to time I am asked which Conn models are considered "professional" models and which models aren't. In the following I shall attempt to answer this question.

1915-1949
This period saw many musicians who played at a professional level. As a result and as far I can tell, almost all Conn instruments produced under the "C.G.Conn" brand were professional level instruments. The differences between the models were mostly related to features with models tailored to orchestral playing, jazz, etc. Also some preferred large bores, others smaller bores. Some models might have possessed additional features making them slightly more expensive, but as far as I know there were no "student" models produced under the C.G.Conn brand. These student models were sold under the "Pan American" and "Cavalier" brand of instruments.

1949-1955: Transitional period
The period between 1949 and 1955 shows a transition between the "old" and the "new" way to doing things. Instruments with the same names (Connstellation, Connquest, Director), as in the following period (1955-1970) should be counted in that period with the exception of the "Victor" and "Artist" instruments. These "Victor" and "Artist" models as well as the other instruments belong to the previous period. Especially 1954 and 1955 are watershed years. The Pan American division disappeared (for all intents and purposes) and Conn started producing student and intermediate level instruments under the C.G.Conn brand. The few instruments still surviving from the previous period were restyled and where necessary renamed (80A, 22B).

1955-1970
This is probably the period most people are familiar with. Conn radically changed strategy in 1955 by focusing almost entirely on the school band program as opposed to the professional, orchestral player. Conn's naming convention during these years is very consistent:

Connstellation Always the top of the line and most expensive instruments. Although Connstellation models were used by several very well known people (Maynard Ferguson: 38B, Cat Anderson: 38B, Thad Jones: 28A) they didn't have the following enjoyed by Conn instruments in the 1920 and 1930's.
Victor/Artist The Victor and Artist names are used somewhat interchangeably, as is evidenced by the fact that from 1959 the 10B is a "Victor" while the virtually identical 10A is an "Artist" model. Either way, these are one (small) step below the Connstellation models. Seen by some as "cheap Connstellations", although I disagree with that. Between 1955 and 1957 the 6A/6B and 10A/10B Victor models were very different instruments from the 38B/28A Connstellation. While it is true that from 1958 the 6A/6B and 10A/10B were redesigned to resemble the 38B and 28A Connstellation, to say they were "cheap" versions of the Connstellation would be unfair towards the 6A/6B and 10A/10B. Interestingly, Victor/Artist model trombones enjoyed much greater popularity than the 48H Connstellation. Apparently trombone players realize there is more than just "Connstellation".
Connquest The intermediate level instrument. Contrary to modern intermediate level instruments which are often described as "student models with first slide saddles" (in the case of trumpets), the Connquest really was a step in between the Victor and the student model Director. I have played a 15B Director for over 20 years, and have owned a 6A Victor long cornet since 2002. In early 2003 I had the opportunity to try out a 1959 77B Connquest. Without a doubt it was better than the 15B Director, but not quite up to the level of the Victor.
Director The student model, cheapest Conn model. In 2000 I was in a music shop and tried out a brand new UMI-Conn 22B Director model (no relation to the venerable 22B New York Symphony/Victor). I don't want to offend anyone, but it couldn't hold a candle to the old 1960's 15B Director.