Do fuel injectors have built in filters?

[Sunroof]

I have a 1973.5T with the 2.4 and CIS. My injectors (911 110 355 01) are rare, or that is they were manufactured on a six month run and only for the 73.5T.

My Porsche shop identified one injector that did not spray but rather poured, so it was replaced. The others were sent out for injector service (cleaning and spray pattern check) but I have to wonder just how successful that was! I still experience a slight bump or hesitation in the lower RPM range but seems to be fine at higher rpms.

I was also told that injectors have a built in filter, which might have some deposits causing the issue and was advised to keep using concentrated fuel cleaner (Chevron Techron or Sea Foam, etc), which will eventually clear up the problem.

My question is: Do these injectors really have an internal filter? and why are these so darn expensive? Around $250 each on average.

Thanks