Most of them are clearly signed:
A469: https://www.google.com/maps/@51.6727839,-3.218459,3a,75y,201h,73.25t/data=!3m6!1e1!3m4!1sIcs0KjDgZ1YGXF4lWN9Mjw!2e0!7i16384!8i8192
B4242:
https://www.google.com/maps/@51.7354537,-3.6461222,3a,75y,66.66h,90.42t/data=!3m6!1e1!3m4!1sKqpr1fX1qC9IlkVz_XY6sw!2e0!7i13312!8i6656
B4246:
https://www.google.com/maps/@51.8235274,-3.0912766,3a,75y,77.33h,84.63t/data=!3m6!1e1!3m4!1sBRDhG5BZgBcWC2rWiTIslA!2e0!7i13312!8i6656
B4251:
https://www.google.com/maps/@51.6787011,-3.1382943,3a,75y,332.53h,87.28t/data=!3m6!1e1!3m4!1sxt6Q3bwtVlnmYe4ofZ5NaA!2e0!7i13312!8i6656
B4257:
https://www.google.com/maps/@51.7677895,-3.2952615,3a,75y,112.28h,74.33t/data=!3m6!1e1!3m4!1s6wzGrfQa8DWzdLdPEd4ErQ!2e0!7i13312!8i6656
All signed
towards the mainline, and the B4521 one you've put at a junction at the end of the route in the browser, not the route you want added as a branch, so it's not only towards the mainline, but is signing the actual mainline.
These are also often the only sign, despite many of these branches TOTSOing and so work as just a vague "this way to that road" sign (eg B4257). Add in that many of the routes of these branches are now
traffic calmed, and perhaps with
through traffic dissuaded (one that michih suggested adding recently), and it strikes me that they are effectively outdated/erroneous signs. Others (eg B4242) are a link road with no intermediate junctions - and if we add them, we need to add the
M5 trumpet sliproads at junction 22 as its signed as M5 towards the M5 - and probably twice given it's signed as part of the
A38 off the M5 mainline!
I do not believe that a unbracketed route number on a sign is adequate evidence of a road being inherently part of that route. For instance the road between the A465/A4143 junction and the B4246/B4269 junction is signed southbound as
B4246 (which is the correct number), and northbound as
A4143, the latter being not true, though if you go that way you will inevitably end up on a bit of road designated A4143. And
here we have a sign for the A4059 on a road (that you missed) marked by OSM and GM as a branch of the B4275, but the
other end has no number - what is that? I'd say it's a link road, not a branch of either road.
I'm not going add what is probably 2000 routes (you suggested 7 off about 50 routes, and you only mentioned about half such branches off those roads!), mostly poorly (and even incorrectly) signed and many of which are mapping errors, without quite a lot of justification. Spurs in the UK have to be signed, and signed
heading away from the mainline otherwise we enter madness.
I should point out that I went to a lot of effort to work out whether to add most of these specific branches when drafting the system. I'm not going to take "OSM and GM show it" as anything serious - and expressed such in the last message before this Wales review (thank you, by the way - it's much appreciated). I'm going to need some evidence it should be included beyond unreliable mapping sources, otherwise I'll just ignore it from now on.
Edit: adding the A469 branch as there is actually a sign pointing away from the mainline with that number on:
https://www.google.com/maps/@51.6705061,-3.2238246,3a,75y,78.59h,80.61t/data=!3m6!1e1!3m4!1sMDAv5x5k6zFbW-7wLhY4QA!2e0!7i13312!8i6656
