This is a typo that was introduced in the 24th Edition. ARR is omitted from the list of prefixes on the first row of page 313 (of the 28th Edition). It was present in the same list of the 23rd Edition.
Logged
BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.