"Did phones with these sets originally have some sort of blocking insert...?"
No.
BTW, the phones with the ribbed faceplates are much more desirable to collectors than phones with the later opaque ones.
Originally, the faceplates were all charcoal gray, then they began to be issued in the muted colors that complement the housings.
Even though the very early phones had the gray faceplates, they are in less demand than the ones with the various colors.
Any phone with a 10-button dial (type 25) rather than the 12-button dial (type 35) is more sought after, regardless of the faceplate color.