I don't know very much about old Halloween postcards, but would be willing to bet that all of these post cards were originally printed before 1930, but then again some could be reproduction, they aren't mine, and I really wish they were.
Over time and with not much difficulty I have found postcards for every holiday, birthdays,and just to keep in touch, some with messages as diverse and love poems , directions to a train station and what covered dish the recipient should make for the family reunion, and a message about the new "egg man" in town.
Every holiday except Halloween that is. Perhaps they were all grabbed up by collectors, and perhaps they weren't saved from year to year, and it just could have been that there just weren't as many sent for Halloween.
They cost a penny to mail, but I don't know how much the cards themselves cost. Apparently not everyone had phones yet. People often wrote letter to friends and relatives, even if they lived rather close by.
The images on these cards seem to be designed for adults as well as children.
Bats, witches, cauldrons and jack-0-lanterns, children celebrating, black cats and brooms, everything is there. All there under the full moon, and shooting star.