It's always risky to make sweeping generalisations, if only because some smart-arse will come along with the exception that proves the rule.
The WD Serial numbers were commonly referred to as 'census numbers' back in the day. Prior to mid 1940, these were applied after delivery, either by the RAOC at Chilwell or by the signwriters of Ally Sloper's Cavalry at any of their various depots.
From mid-1940 onwards, the manufacturers appear to have been paid 1/- per machine to apply census numbers and in general these were sign written. However, the style varied from manufacturer to manufacturer and certainly in the latter stages of the war, it would seem that some used transfers.
Presumably the printers had developed a technique for producing consecutively numbered transfers on backing sheets.
The only way to be sure about these things is to look for period photos of bikes from the same contract and then to analyse the font types. I could give you chapter and verse on early / pre-war Nortons but late-war Triumphs are not really my thing...
I totally agree Rik. I avoid comments that state something did or didn't happen for sure..... because I wasn't there!
I have been criticised for using this font, which I like. But I've seen it in original pictures and available from Axholme in laser cut low tack stencils.......No commission in it for me either 
Ron
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email (option): ronpier@talk21.com
No offence Ron, you know me! Just love to stir things up sometimes, to get more answers, and Rik provided a nice one! (please have the early Norton stuff on mu desk by 9.00 Rik!!
Welbikes for sure used transfers, there are enough original paint survivors (MKII's) to show this, but it's not sure if varnish or water slide transfers were used.
MKI's were stencilled;
Cheers,
Lex
This time the code, while I know for sure I had it right every time, took me over 25 times, this is really insane!
email (option): welbike@welbxxx.net
None taken Lex. You know I can give as good as I get
Can I ask? What is the number on the tip of your front guard? and is the transfer on the side car mudguard some artistic license, or a correct feature? Ron
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email (option): ronpier@talk21.com
Ah, so on the receiving end here?? 
The number on the tip of the front guard is the embarkation code, Rik found out about that one, it's copied from an original picture of the TT Division.
So far so good, now the names can come under the "Artistic Lisence" chapter, but from 1940, March the 18/19/20th. to be precise!
See also Rik's posting here:
http://pub37.bravenet.com/forum/static/show.php?usernum=3155626639&frmid=16&msgid=1324866&cmd=show
For the filming of the propaganda film, the Squaddies, sorry Fuseliers, thought they would give their loved ones at home a nice surprise, with chalking their names on the front number plates, incredible they got away with it!!
Tess, and Doris can be seen here, but Jess was also used, with a variety of other womens names.
So since not my B4 in the picture but Alexanders, he chose to paint Jess on, as that's his girlfriends name, have told him it should be chalked, instead of painted on, and will be rectified in due course.
Then the mudguard transfers, you are right here, pure artistic license!! but Dave Horror and Rik had found out recently that a black bordered gold Norton transfer was used on the tailpiece of the 16H, they cut that bit of with the B4, and none can be seen on period pictures. (will check though)
Any more questions??? 
Cheers,
Lex
email (option): welbike@welbxxx.net
Here the above mentioned transfer, on a Big 4, but the first contract (1938) long model tail piece, like the 16H.
Cheers,
Lex
email (option): welbike@welbxxx.net
Then the mudguard transfers, you are right here, pure artistic license!! but Dave Horror and Rik had found out recently that a black bordered gold Norton transfer was used on the tailpiece of the 16H, they cut that bit of with the B4, and none can be seen on period pictures. (will check though)
Cheers,
Lex[/quote]
Eh..? Are you saying they didn't have the black edging on the mudguard transfer on the B4..? You're picture clearly shows there is a black edging.
That should be rephrased to "you've" just found out Lex, we've known for a long time
It's not often I know something you don't, and in fairness, Rik told me the transfers to use when I restored my bike a few years ago. Here's the mudguard tail piece transfer on the Classic transfers website. So we haven't solved a mistery, they knew about it too
http://www.classictransfers.co.uk/pages/gallery/norton-6334-65x20mm-pound2.25-each454.php
email (option): horror@blueyonder.co.uk
No sorry, they cut off the bottom of the tailpiece (where the transfer normally goes) not the black of the transfer.
And you're right, but didn't know you knew that for years already.
But I sure didn't know about the black edging!! hey I can't know it all
See difference in length here;
Cheers,
Lex
email (option): welbike@welbxxx.net
Ah, I see what you mean now Lex, thanks... see, I'm learning something every day The trouble is it pushes some old information out of my brain
email (option): horror@blueyonder.co.uk