Could I have a little more?
Sometimes one comes across letters where one wonders: have the rate and duty been applied correctly? Like with a letter that was sent by registered mail from Winschoten to Stuttgart in Germany on December 29, 1927.
Franked with a complete series of children's stamps from 1927, additionally franked with one cent. To determine whether the rate and duty are correct, one must have access to rate lists from that time. I found the following data: The letter rate up to 20 grams to abroad was 15 cents from October 1, 1925, to October 30, 1928. This therefore matched the 15-cent children's stamp. The registration fee was also 15 cents from March 1, 1921, to October 30, 1928. However, the total amount of the three other children's stamps was 14.5 cents. So, half a cent short. Why then was 1 cent added and not 1/2 cent?
The reason is actually very simple: the post office in Winschoten probably ran out of half-cent stamps. For the last stamp of that value was issued on August 1, 1899, in the so-called 'Vürtheim' type.
It was not until January 30, 1928, that a new stamp of the 'Flying Dove' type was issued. So the official saw no other solution than to politely ask the customer 'if it could be a little more,' and affixed the 1-cent stamp, which was readily available. When participating in stamp exhibitions, displaying overpaid letters is strictly forbidden. But with a good explanation, as described above, they are perfectly usable!
But could the individual stamps from the children's stamp series actually be used for specific rates? That, too, can be verified using rate lists. The 2-cent (+ 2-cent) value was intended for printed matter up to 20 grams within the Netherlands.
The value of 5 cents (+ 3 cents) was for domestic postcards.
The 7½ cent (+ 3½ cent) stamp for a domestic letter up to 20 grams.
Finally, the 15 cents (+ 3 cents) for a letter up to 20 grams to a foreign country. The letter with the complete series of children's stamps with an added one-cent stamp is sometimes called 'artificial work', but in this case, it is franked perfectly correctly. 
I have also heard another explanation. It is said that an internal PTT regulation was established whereby the civil servant at the counter was allowed to sell a one-cent stamp for half a cent. The missing half cent then had to be accounted for on a form to balance the stamp fund. I have not been able to find anything about this so far.
I have seen the 1 cent cut diagonally on a stamp from our Overseas Territories.
In the Netherlands, the use of cut-up stamps as postage has never been formally permitted. However, it was allowed in Curaçao in 1918, where 2-cent and 2-cent numeral stamps, when cut diagonally, were valid as one-cent stamps due to a shortage of stamps in those denominations.