The list of Letterheads available in the Preferences is quite restricted. Just one example, “Wild Confetti” is not available. I checked the design, and the resources are there - the just don’t show up in the Preferences.
Turns out that the list is hard-coded in the DefaultLogo field. To alter it, just change the listbox lookup in the (Calendar profile) form to
No Letterhead|StdNotesLtr0
Adirondack Chair|StdNotesLtr28
Architect|StdNotesLtr16
Bouncy Earth|StdNotesLtr1
Buck Rogers Mail|StdNotesLtr2
Clouds|StdNotesLtr8
Computer Chip|StdNotesLtr3
Decco|StdNotesLtr4
Envelope|StdNotesLtr25
Falling Spheres|StdNotesLtr5
Fishing Gear|StdNotesLtr23
Frank Lloyd|StdNotesLtr7
From The Desk|StdNotesLtr8
Gateway|StdNotesLtrGateway
Geometry |StdNotesLtr9
Golf|StdNotesLtr5
Gray Gradient with Lines|StdNotesLtr13
Green and Yellow Diamond|StdNotesLtr14
Leaves|StdNotesLtr6
Maple Leaf|StdNotesLtr6
Marquee|StdNotesLtr34
Metal Plate|StdNotesLtr15
Pencil and Grid|StdNotesLtr16
Pony Express|StdNotesLtr17
Post Mark|StdNotesLtr33
Primitive|StdNotesLtr20
Purple Geometry|StdNotesLtr18
Slashed Lines with Globe|StdNotesLtr21
Squiggle with Backdrop|StdNotesLtr22
Squiggly Line|StdNotesLtr23
Surfboards|StdNotesLtr14
Tacks|StdNotesLtr24
Tape|StdNotesLtr25
Teal and Yellow Lines|StdNotesLtr26
Three Dimensional Relief|StdNotesLtr27
Torn Paper|StdNotesLtr28
Triangle with Dots|StdNotesLtr30
Triangles|StdNotesLtr29
Wild Confetti|StdNotesLtr32