My memory might be fuzzy but I remember reading a ad for the set and I would have swear it was called a valve guide broaching. but knurling would make more sense. but it is still not adding but just grooving. a normal example of knurling would be the grip part of a jack handle. normally made with a wheel pushed into the rotating steel from a lath or NC mill the wheel has the pattern, looks kinda like a flint wheel off a lighter.
I think of a normal broach as the things used to make a keyway. so when used in odd ways I get confused I guess
As for the tap method it is not a time saver but a head saver and I think that method had been around a long time so it is a tried and true method.
but a normal shop, time is $ and just a quick pound out is faster.
I saw this tap method used on rare fragile air plane heads. the other method was to bore the guides paper thin and collapse them but that had other risks.
So it is not just the one place that does it like that.
and I think I have also seen that method in a car OEM shop manual too just can't remember which one.
The one thing I have noticed over the years anything to do with machinery have been done. maybe forgotten but done before.
So many times I see something as a brand new then see a 100 year old example latter.
Then there is the term more then one way to skin a cat.
there are a lot of ways to do some things none of them wrong.
and the fastest/cheapest way will become the norm but it might not be the best way but not wrong ether.