Oddly enough, they can ALL be correct! Or explained.
Let's be clear on terminology first. For rate purposes, "post card" and "postal card" are specific defined mail pieces, typically a thin card stock, either single or double (reply) in format.
There is no such thing as a "heavy postcard" in rate terminology. Most U.S. tourists would call these mail pieces a "postcard folder". Anyway, regardless of what anyone calls them, they are not mailable at postcard rates. They require letter rates, most often mailed at first class surface, first class airmail, or 3rd class.
Here are 4 corners of unmailed U.S. postcard folders:
Item 1: published before April 15, 1925, with 1 cent 3rd class or 2 cent letter-rate for first class, depending on writing.
Item 2: similar, but on/after April 15, 1925, with 1-1/2 without message (for 3rd class and 2 or 3 cents as a letter if a message was added.)
Items 3 and 4: Generic information, not very helpful.
To get back to your postcard folders.
In the Prexie era, folders could be sent anywhere in the world without any additional message inside
for 1-1/2 cents as a single piece 3rd class rate, which is where your 1-1/2 cent folder applies. Most folders were constructed with a flap which tucked in, but did not seal, and is consistent with 3rd class mail regulations allowing for postal inspection for possible upgrading to first class if improper writing is found inside.
Folders with a message
would require the appropriate domestic or foreign letter rate postage, which is where your 5 cent and 3-paid/+due folders properly apply.
The 3 cent San Francisco folder is the challenge. With the information you have provided (minimal writing and less than 2 ounces), it would be a single piece, 3rd class letter properly rated at 1-1/2 cents, and overpaid by the sender typically as a "convenience overpayment" exactly as Parcelpostguy suggests.
Tourists seldom have correct stamps handy and find it difficult to obtain them when travelling. Both of the 3 cent mailings may have been thinking the folder WAS rateable as a postcard and the 3 cent international UPU card rate applied, but they were mistaken. Due to the presence or absence of writing, the San Francisco folder was overpaid and the Cleveland folder was underpaid!