Alden has produced thousands of models over the years. Each model has a somewhat unique combination of style, shoe last, upper leather, welt, and outsole. This combination is referenced by a model number. If you know the model number, this website can help you identify the all those characteristics of the model.
The information in this post was pulled together using information in my Alden model database and from the contributions of JSO1 over at StyleForum. See his excellent analysis here.
Location of the model number
On an Alden pair of shoes, there will be a few groupings of numbers and letters on the inside of a pair. The model number will generally be on the second line in the center. Model numbers sometimes have prefix and suffix values that provide additional information the pair.
Model Number Prefix Values
Below is a list of the prefix letters that have appeared in the pairs indexed in the past five years. Most of the prefix values represent a country or regional restriction.
A = Asian model (non-Japan) / Brooks Brothers models
Models made for the Asian market. Two vintage Brooks Brothers Shell Cordovan models also use the “A” prefix (A764 and A765).
Example: 
B = ????
No idea on this. I doubt B is for Brunei.
Example: 
C = ????
Three models have appeared on ebay in the past years with the “C” prefix – C906, C907 and C909. The models appear identical to the standard 906, 907 and 909 models.
Example: 
CU = Custom
A custom pair. Generally these are boots but other styles have appeared on eBay during the past five years.
Example: 
D = USA model
Models made specifically for the domestic USA market. JSO1 breaks this number down further in his post.
Example: 
G = Canadian model
Models sold by Canadian retailers.
Example: 
H = Cape Cod Collection
Collection of casual shoes made in Maine.
Example: 
M = European model
Models sold by European retailers.
Example: 
N = Japanese model
Models sold in Japan.
Example: 
RX = ????
No idea on this code. Just one model has used it (RX10)
Example: 
SM = Sales and marketing?
I believe these are test models for sales. They typically have a two digit year suffix.
Example: 
T = Trial
Pre-production pairs made by Alden. The “T” is usually followed by a two numbers which represent the year of the trial pair.
Example: 
Z = ????
Just one example of a “Z” prefixed model has appeared on eBay (Z54321). The meaning of the Z is unclear.
Example: 
Model Number Suffix Values
The suffix values generally distinguish particular construction features of a pair. What can be confusing is that models can appear with the same construction features and not receive the suffix.
A = ????
“A” has graced one model, the 9951A.
Example: 
B = ????
Just one model has used the “B”, the 9245B.
Example: 
C = Commando Sole
The pair has a leather sole with a recessed rubber lug overlay and a lug rubber heel.
Example: 
D = Dainite Sole
Studded rubber sole made by Dainite of the UK. The “D” also appeared on a pair of boots made for Epaulet that did not have a Dainite sole (D5836D).
Example: 
E = Exposed Eyelets (?)
E has appeared in just four models. It appeared in two models with exposed eyelets (9707E and 96080E). The “E” suffix was also used on two pairs of sneakers (1952E and 1958E) that did not have exposed eyelets.
Example: 
F = Flex Welt Sole
Oil soaked sole. Generally with single leather thickness. The “F” suffix was also used on a few early commando pairs (1304F, 1724F, 3314F and 3316F)
Example: 
H = Speed Hook
The top four eyelets on a pair of boots have been replaced with hooks.
Example: 
L = Leisure
Leisure rubber outsoles
Example: 
M = Meier (retailer)
Pairs made for Eduard Meier of Germany.
Example: 
R = Rubber sole
Rubber soled pairs.
Example: 
S = Lug Sole
Pairs with a thick rubber lug sole. Yes, that’s an “S”, not an “8”. An exception is the D5703S which has a Waterlock sole.
Example: 
U = Unlined
Pairs that are fully or partially unlined.
Example: 
V = V-Cleat?
“V” prefix was given to a 990 model with V-Cleat (990V)
Example: 
W = ????
The mysterious W has been imprinted on two models: 3643W; 3625W.
Example: 
X = ????
The “X” has appeared in a mocc toe dress shoe (209X), and an awkward pair of sneakers (225RX), and a recent model from Leather Soul (D9301X) .
Example: 
Y = Extended Welt Sole
The sole is sightly wider than normal.
Example: 
Hello
what do you say about an Alden model, kind of 2145 but a serie model 14901. It is currently on Ebay. The size is 8 M
so it is a little bit unusual so to say, best Vincent
Great resource, this site. Thank you! A couple of caveats: not all unlined (partially or otherwise) models contain UF. This is certainly true of non-stock makeups by retailers. I.e. La Rossa, and I think Brick and Mortar, have unlined models that do not contain the U – only F.
Thanks. There are definitely some inconsistencies with the numbering scheme.
The post is awesome! Unfortunately the picture is not working, can you update the picture? Thank you!
Thanks. I fixed the images and links.