It appears I have opened a can of worms!
My understanding of the valances is as follows:
Part Number 814529
The original front valance, holes for the front under riders and front triumph badge included, no mountings for a spoiler.
Used on very early Dolomites and Toledos, don't know about the 1500FWD.
As far as I can tell, this is universal to the entire range INCLUDING the SPRINT. It is listed in my Sept 75 Sprint parts list as being correct for all Sprints up to VA 15000 (around the publication date of the book Sept 75) In fact the series 1 Sprint only went to about VA10450, then a gap was left and series 2 production began at VA15000 with the XKC0504 valance as OE. Not sure what they did at the factory, but i'm fairly sure that replacement valances of ANY part number didn't come with holes for the upper nose badge, OR the centre one, which MAY account for the considerable disparity in position of this badge between individual cars. Further to this theory, I recently got hold of a NOS Toledo bootlid which had NO holes predrilled for any of the badges or moulding strip fitting clips. Not wanting to build in any more rust traps, I left the strip moulding off and removed the pins and stuck the badges on with double sided tape!
Part Number XKC0504
Holes for the front under riders and front triumph badge included, mountings for a spoiler.
Used on early 4 Headlamp shells (Dolomites, Sprints. 1500) and Toledos.
Despite the picture in the parts list showing them, XKC0504 does NOT have holes for under rider brackets. I'm a little confused as to why your Nov 74 car has these holes and my Dec 73 car didn't! I removed the rotten remains of mine to fit a club GRP one and i'm certain it wasn't a later replacement, all the spotwelds checked out as original.
Part Number ZKC2657
No holes for the front under riders and front triumph badge included, mountings for a spoiler.
Used on Dolomites and very late Toledos, introduced sometime in 1975 / 76
Most new old stock valances are likely to be these as they continued to be made sometime after production stopped.
As far as I can ascertain, this is XKC 0504 just with a different number and purely a book keeping excercise during BL rationalisation. The NOS one of these that I have, dating from 1989 (sticker still legible) has no holes for under riders OR ANY nose badge, does have holes for spoiler but no really noticeable swage at the lower edge, just a very faint crease at the outer edges where the valance flares a bit to equal the wing length. I'll try and get some pics when there's daylight but the brown primer finish doesn't make it easy to get precision pics.
Regarding the lip or lack thereof for mounting the spoiler, my Toledo is fitted with part number XKC0504 (November 1974 build), so the middle of the three known valance variations, it has the under rider holes, badge holes and mountings for a spoiler. If you look at it closely you will spot two design elements which I think are pertinent, firstly when looking from the wheel arch down on to the valance wing join the valance protrudes approx 25mm further back horizontally, secondly if you look at the valance from below corresponding to this extra 25mm there is a swage line running the width of the panel. I have included a couple of photos of my Toledo below to illustrate this (both panels are the original items on the car).
Please excuse the dirt, but I believe in using my car all year round and it was cleaned on the weekend.
If you look at period photos of the very early cars (J reg or thereabouts), I have not been able to see the swage line running across the width of the valance, and it appears the valance ends in line with the wheel arch. I could be wrong but I believe the valance was extended back approx 25mm, and the mountings added for the spoiler to change part 814529 into XKC0504. This I believe is why the valance protrudes further back in relation to the wing than you would expect, rather than retool the wings Triumph just added a chamfer to the edge of the valance.
The next problem is when was the change made, and what is appropriate for a K reg Toledo, it looks to me like the valance in this picture below if you extrapolate the edge to take into account the missing section would be in line with the back of the wing.
I reckon the correct valance for a 72 car would be 814529, but I too would leave well alone, now that it's painted!