The Belgian kennelclub use every year the next letter of the alphabeth, so every year is a other letter, even if you have more litters of no litters in that year, the alfabeth continiues.

Every breeder and litter in belguim gets the same pedigree letter. Our last litter is from 2019, so the S letter we have to use

2019 : S Litter 

2020: T Litter 

2021 U Litter

2022 V Litter

2023 W Litter