1970s Stamp Collection Lot of 18 Postmarked Stamps Lancaster Pennsylvania

Description

1970s stamp collection of 18 Postmarked Stamps.
Found these in my grandfathers old desk cleaning out some old stuff.
I don’t know much about stamps and have no idea if these are valuable.
They are all on the ripped off corner of an envelope, seem to be in pretty good condition.
They are all postmarked from 1973-1978 with postage cost at 8 cents to 13 cents
List of stamps:
Clara Maas she gave her life 1977
Centennial of sound recording x4 1977
Pueblo Art x2 1977
US airmail 1977
Christmas Rafael national gallery of art 1973
Olympics 1976
Christmas - Early card by Louis Prang
Harry S Truman 1973
Apollo Soyuz 1975
Commercial Aviation 1976
Christmas Nativity scene x3 1977
Christmas people hanging out at a frozen lake? 1977
Thanks for looking!