For the records, there are about fifty old coins (6)
I believe the answer is:
annals
'for the records' is the definition.
(I've seen this before)
'there are about fifty old coins' is the wordplay.
I cannot quite understand how this works, but
'are' could be 'a' (short for 'are', historical unit of measurement) and 'a' is present in the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is found within the answer.
'fifty' could be 'l' (Roman numeral) and 'l' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for annals that I've seen before include "Historical records" , "Records of past events" , "The Four Masters wrote them in 17th century" , "Archives" , "Yearly records" .)