I drove the road in both directions today. It's only signed IC20. I couldn't spot any A38 sign! It's also confirmed by
wikipedia.
Actualmente, a A 38 ainda não está sinalizada como autoestrada, mantendo a sinalização a nomenclatura IC 20.
I guess there might be more IC roads which officially have an A numbering but only IC numbering signed. I didn't drove A37 but it's only signed IC19 on A9. OSM indicates A37 and IC19 like it's also done for A38/IC20.
Wikipedia doesn't mention it.
According to wikipedia,
A34 seems to be IC8 only. OSM confirms it.
According to wikipedia,
A35 seems to be IC12 only. OSM confirms it.
A36 is only called IC17.
A39 seems to be IC21 only.
There might be more, e.g. A31 according to OSM...
A33 is signed on IC20 exit