There are way too many variables to what make national note valuable. Over 14000 banks issued notes. You are most likely going to have to find a web site or perhaps a book to help you with how many notes those banks printed.
If I had to guess though...
The Plattsburg 20 Twenty was made late in the era of Nationals making it more likely that notes survived. However if you take the serial number and multiply it by 12, because that note was printed on a sheet that contained 12 notes, it leaves us with a minimum of 15,000 notes printed. That number is very small and could make it quite rare, or it could just mean it was one of the earlier notes printed for that bank. Also the bank is from a relatively unheard of city. In fact if you were to type it into a google search you would find the city name misspelled because Plattsburgh contains a h at the end. Only three charters were given out for Plattsburg NY, but this bank was the first issued a charter. That could make it rare or it could make it more common. I can't quite make up my mind about this one but I would guess it to be rareish. Again that is just a guess.
The 5 from Providence was printed on sheets of four notes. If you take the bank serial, the number under the portrait, and multiply it by 4 that gives you 435,828. That number is the bare minimum number printed based on this note. That makes it a little more common: plus the fact Providence is a pretty big city that had 30 bank issued charters. This note I would guess to be a more common national note, but as I've stated before in this post this is just a guess for fun.
Both these notes are awesome looking and I would love to have them

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Edited because originally I posted the Plattsburg twenty to be printed on sheets of 8 notes, but in 1929 that number was increased to 12 along with a host of other changes. Sorry for the mess up

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