The first  two digits of the product code for each piece of sheet music indicates its instrumentation category.
i.e. 01C030001605 is the code for Poulenc’s Sonata for flute & piano. The bold digits (01) indicate the instrumentation category. See below.

01 – Flute & Piano
02 – Cadenzas
03 – Flute Alone
03A – Flute Alone (Collection Books)
04 – 2 Flutes
04A – 2 Flutes (Collection Books)
05 – 2 Flute & Piano
05A – 2 Flutes & Piano (Collection Books)
06 – 3 Flutes
06A – 3 Flutes & Piano (Collection Books)
07 – 3 Flutes & Piano
08 – 4 Flutes
08A – Flute Flutes (Collection Books)
09 – 4 Flutes & Piano
10 – Flute Choir
10A – Flute Choir (Collection Books)
11 – Flute & Bassoon
12 – Flute & Clarinet
13 – Flute & Tape/CD
14 – Flute & Guitar
14A – Flute & Guitar (Collection Books)
15 – Flute & Harp
15A – Flute & Harp (Collection Books)
17 – Flute & Organ
17A – Flute & Organ (Collection Books)
18 – Flute & Percussion
19 – Flute & One Wind
20 – Flute & Two Winds
20A – Flute & Two Winds (Collection Books)
21 –  Flute & One String
21A – Flute & One String (Collection Books)
22 – Flute & Two Strings
23 – Flute, One Wind & One String
24 – Flute, One Wind & Piano
25 – Flute, One String & Piano
27 – Woodwind Quartets
27A – Woodwind Quartets (Collection Books)
28 – Flute, Two Strings & Piano
29 – Flute & Three Strings
30 – Mixed Quartets (Winds & Strings)
30A – Mixed Quartets (Winds & Strings – Collection Books)
31 – Mixed Ensembles (5 or more Instruments)
31A – Mixed Ensemble Collections
33 – Woodwind Quintets
33A – Woodwind Quintets (Collections)
34 – Flute & Voice (with and without accompaniment)
35 – Miscellaneous Ensembles
36 – Flute with Band or Orchestra
37 – Alto Flute & Bass Flute (with and without accompaniment
38 – Piccolo (with and without accompaniment)
39 – Irish Flute, Pennywhistle, Tin Whistle, Fife, Pan Flute, Ocarina
40 – Flute & Piano Collection Books
41A – Christmas & Hanukah Music – One Flute (with and without accompaniment)
41B – Christmas & Hanukah Music – Two Flutes (with and without accompaniment)
41C – Christmas & Hanukah Music – Three Flutes (with and without accompaniment)
41D – Christmas & Hanukah Music – Flute Flutes (with and without accompaniment)
41E – Christmas & Hanukah Music – Flute Choir (with and without various instruments)
42 – Blues, World, Jazz, Pop, Rock
43A – Sacred – One Flute (with and without accompaniment)
43B – Sacred – Two Flutes (with and without accompaniment)
43C – Sacred – Three Flutes (with and without accompaniment)
43D – Sacred – Four Flutes (with and without accompaniment)
44 – Methods & Studies
45 – Fingering Charts
46 – Orchestral Excerpts
46A – Kalmus First Flute Folders
46B – Megido Complete Orchestral Parts
47 – Native American Flute
48 – Literature (Books, etc.)