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No clues on the first pic posted?
All of us are a bit handicapped to offer advice without knowing what reference source you are using to attempt these identifications, thus it is hard to know where to start from. A printed catalog, an online listing/database,
ebay or ?
The first two stamps can be narrowed greatly (if not totally) by the perforation rate and format (sheet, booklet, coil), in fact the second can only be the coil 599. The first has several lookalikes.
Don offers sage advice to first assume each stamp is the most common type, then work forward. The US is a large, literate country and most US stamps of the twentieth century are printed in very large quantities to be the workhorse issues of their respective eras. The exceptions are rare because of exactly that - they are rare, and will not typically be found in small beginner accumulations. We are talking odds in lottery winning terms. You are more likely to be struck by lightning.