German serial numbers normally went only to 9999 before adding a letter and reverting to 1.* They went 1 - 9999, then 1a - 9999a, 1b-9999b and so on.** Each manufacturer started over each year. So a full description of a German weapon would be something like "K.98k, made by Mauser (code byf), dated 1943, serial number 1234c"
*Mauser did make some rifles with 5 digit numbers.
** Leading zeros were not used, causing some owners to believe they have a very early rifle ("how can one of the first Mausers ever made be dated 1942?") when they do not.