Complex sentence: The current circulating coin was introduced on 11 February 1991 to replace the existing $1 note, although there had previously been occasional issues of commemorative "silver dollars", but they are rarely seen in circulation.
Split into simpler sentences: The current circulating coin was introduced on 11 February 1991 to replace the existing $1 note. There had previously been occasional issues of commemorative "silver dollars", but they are rarely seen in circulation.