Canadian Precancels

I've just been going through an envelope of extra Canadian stamps and found a number of George V and VI precancels. As you all know, I'm sure, we here in Canada were secretive about our precancel locations and used a numeric code.
I know next to nothing about these things. Can anyone tell me a) why we used numbers while our American friends printed the city of origin b) is there an easy to access list of what these numbers mean and c) - and I think this has been answered on another thread - if a stamp is precanceled but still has it's gum, is it considered used?

This may not be a complete list, but it's what I have for Canada precancel codes:


CANADIAN PRECANCEL STAMP CODES

NOVA SCOTIA
X275 Halifax Nova Scotia

NEW BRUNSWICK
X809 Moncton New Brunswick
X910 St. John New Brunswick
X945 Sackville New Brunswick

QUEBEC
0592 Lennoxville Quebec
0700 Montreal Quebec
1050 Quebec Canada
1142 Rock Island Canada
1470 Saint Hyacinthe Canada
1810 Sherbrooke Canada

ONTARIO
2186 Beamsville
2310 Brantford
2342 Brockville
2450 Carfleton Place
2575 Cobourg
2980 Galt
3080 Guelph
3100 Hamilton
3340 Kingston
3366 Kitchener
3445 Lindsay
3070 London Ontario (Error, should have been 3470)
3470 London
3800 Niagara Falls
3893 Oshawa
3900 Ottawa
3975 Owen Sound
4004 Paris
4035 Peterborough
4260 Saint Thomas
4530 Toronto
4900 Weston
4940 Windsor
4970 Woodstock

MANITOBA
5099 Brandon
5850 Winnipeg

SASKATCHEWAN
7120 Moose Jaw
7420 Regina
7550 Saskatoon
7977 Yorktown

ALBERTA
8160 Calgary
8360 Edmonton
8605 Lethbridge
8802 Red Deer

BRITISH COLUMBIA
9500 New Westminster
9780 Vancouver
9890 Victoria

jamesw, what you are looking for is The Standard Canada Precancel Catalogue which isn't too expensive. I have a 2000 edition and it was listed for $12.95. Early 1900s Canada precancels did have the alpha name of Canadian cities on the stamps.

Wow, great responses, thanks wt1 and mhc99. But what about part c of the question? I've got three George V 1932 1c dark greens (one a coil) sitting here in front of me, precanceled with gum on the back. Are they used or unused? I'm so confused!!

Jamesw, regarding point "C", the following is extracted from the catalogue I referenced in my earlier posting:
"When a stamp is precancelled it is considered cancelled. Prices in this catalogue are for precancelled stamps without gum. Collectors who prefer stamps (precancels) with gum should expect to pay a premium over the catalogue value"

Well.....so what am I bid? Just kidding.