I've been curious about this issue for some time now. I've seen photos of early (73 and below) climate control heads and late (74 and up) ones. Is there a reason why the later climate control heads don't have the spring detent on the blower speed selection when there is clearly detents in the plastic for a spring detent so you don't over run the speeds? It's as if Porsche completely omitted the little riveted spring detent for the blower motor speed selection detents. Photos pulled from one of the other threads I posted in.

Even with the spring and the ball in place there is practically no feel for correct position
of the control knob for each speed.
That is why most slide contacts are melted and non-functional
Nice NOS piece by the way.
I've got an early one for my early cars.
Rory

It's not my NOS piece unfortunately haha. I just saved the photos, went into Paint and added the arrows to show the differences.

I think it was Porsche saving a few cents on making the heater control panel when the Deutsche Mark was skyrocketing against the US Dollar in the early 1970's in order to keep down the price of 914's in US Dollars. Or maybe they were just listening to Sandy Munro's YouTube channel.

THAT is my early piece !
I think I posted the pic when I was discussing the same issue.
.... I recognise the glass table.

Anyway, I've found that if not too melted the slide contacts can be cleaned up with a razor blade and a file or a rotary disc to restore flatness.
As for detents, an arm from another unit with the leaf spring can installed in any
control panel along with with a suitable ball.
Good luck finding tiny balls.

Every OEM begins to look for cost saving opportunities as a vehicle matures in the market.

OEM's also need to continue to find cost offsets to the continual increase in regulatory burden. Example -- for 74' had to add rear bumperette's. Customers don't want to pay for that. OEM can't be expected to just add regulatory content that customers won't pay for. OEM's go looking for other places to save money that won't be a huge customer pain point to minimize their profit loss.

Elimination of a non-critical stamped steel spring, a rivet, and the assembly cost to install those two parts is good place to save some money.

Elimination of the stamped steel spring also means there is no additional money to be spent maintaining or re-manufacturing that stamping tool which was probably already getting pretty worn by 1973. Same for any of the assembly tooling used to install the rivet.

It is the way the world works.