No, I am sorry but i think you are wrong.
As I say, I worked twelve years at a seat frame manufacturer. If you punch holes into a piece of steel and do the same to every piece of steel whether the hole is needed or not it is cheaper than having TWO production routes where some holes are drilled and some are not. You see, the reason is that there are invariably more than two options so two production flow lines would then feed into two more flow lines which gives four flow lines etc etc. what you soon get is exponential growth in the number of potential production routes. It is far cheaper to make a basic frame, with multiples of holes in, and just bolt a bracket in later down the line if it is needed. That way you have one tool to punch 2/4/6/8 holes etc rather than eight tools each punching one hole. You occupy a tighter production line, with a smaller footprint and with less chance of making mistakes. I wonder how many times a spider was presented with a seat with its belt clips missing?
Had the seat been sourced in the UK I can almost guarantee that it would have had those holes ready to take the bracket even if the bracket is not fitted. That is the cheapest way. It is also one of the many doctrines of the most powerful production system in the world. TPS or the Toyota Production System is the blueprint for virtually every car manufacturer in the world. I had TPS rammed down my throat, because it works!
I recently saw Maseratis being built and they do it the difficult, more expensive way, because they want the product to be thought of as bespoke and hand built. This is one of the reasons they take days and days to build a single Maserati rather than the hours most other producers take and why it is so expensive.
Alfa Spiders, in 1997, were very expensive for what they were ( I think the cheapest was £21k and the most expensive £29k, though I may be slightly out) and they were not claimed to be hand built. They (Alfas)did not sell in huge numbers, which is not surprising, and they are/were never considered one of the world's superpower car manufacturers, even after being bought by Fiat. I reckon the car seat is their typical wasteful approach and is reflected throughout The production of every part they made or sourced. Ergo why they they were so expensive.
It does not make a bad car, in fact I like them so much I bought one. But it does make for quirky technical decisions with inexplicable results. Oh, and it costs more to do.