As Gary (glowe) noted, the plain Patridge sight was the standard throughout the 1930's. Actually it got a flying start, being the standard starting in 1923---and then couldn't quit until 1942!
As far as yours goes, yes, special order; although I don't know that anything was so special about it because it's my admittedly dim recollection you could have any front sight available on any target model just by asking. And having asked, it would be child's play to swap out one front sight for another----admittedly an extra step in the normal process of filling an order, but no big deal.
This tale isn't exactly on point, but it's close enough: I had a .38 S.A. 3rd (Model of '91) Target------with an unnumbered latch----which had my knickers in a knot! Jinks explained the unnumbered latch thus: Having received an order for this gun, and having none in stock, they simply took a fixed sight gun from inventory to the Service Department, and had them convert it to Target----swap out the sights. The Service Department folks work on one gun at a time (therefore having NO parts on their bench from any other gun)--and therefore having no need to spend any time numbering any replacement parts.
Done and done!
Ralph Tremaine
I just thought of something that will answer any of your questions about your sight----when and where did it come from(?).
Any part fit to a frame is numbered. Any part fit to a part fit to a frame is also numbered---and that includes front sights on target guns. If you don't already have one, get a cup tip punch (.040"----from Brownells---a short one) and pop off your front sight blade. If it's numbered to your gun, it was born that way----otherwise it's otherwise!
And yet another afterthought: If the sight was a "special order", I'll bet you the price of the letter (which you will have already paid---so you don't have to pay it again to me if turns out what I say is so) the letter won't say one word about the front sight being a special order---and that's because it's HIGHLY unlikely the factory records from which a letter cometh will say anything about the sight----------'cause it didn't cost anything extra.(!!) That is, of course, unless you prompt them to say something about the sight so you can end up with a freebie letter!! And why not?!! It'll likely be Christmas when the letter shows up, so you'd be entitled to an extra present!