Perhaps you should try some spelling variations:
"chelmsford 17th f.l." » "chelmsford tw f.l.", "chelmsford march f.l.", "chelmsford which f.l."
"chelmsford 17th a.d." » "chelmsford tw a.d.", "chelmsford march a.d.", "chelmsford which a.d.", "chelmsford 7th a.d.", "chelmsford 17th acm.", "chelmsford 17th act."

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"chelmsford 17th f.l.\") OR (\"chelmsford 17th a.d.\"))".
• Removing quotes may allow a broader search: (( chelmsford 17th f.l. ) OR ( chelmsford 17th a.d. )).
• Adding a wildcard symbol may retrieve word variants: (("chelmsford 17th f.l.") OR ("chelmsford 17th a.d."))*.