A denotation of the year in a date; approximate dating by the year only; identification of the year of origin.
Back then, it was something similar to today's lazy people leaving out not only the first digit from the date, but they abrogate the whole century in one swing. I am sure you've already seen in everyday life the misperfection of some people writing only 79 instead of 1979. Or they scribble something like 12/10/11 and are supremely pleased with themselves for how rationalistic they are. They even cannot tell later if their own record meant 12th October, 10th December, 10th November, or some other combination. It's even harder to guess the year unless we know the exact context of the given entry. Was it the year 12, 112, 312, 1012, 1812, 1912? Or 511, 1611, 1711, 1811, or any of the unconsidered remaining deannuations. (Context: Dr∙ Barton and aides are trying to decipher an unclear identification record on an ancient oil painting labelled "415 XI/18". Source: J∙ Okram - The Mystery of the Rammed Key.)
Slovak / Slovenčina (SK): deanuácia; anuitné datovanie; anuačné datovanie; anuácia; ročníkovanie; denotácia ročníka
Czech / Čeština (CZ): deanuace; anuitní datování; denotace ročníku