The abbreviation SF stands for "Schadensfreiheitsklasse". The first year of coverage was 1977 and the insured had 23 years without a claimed accident. (The 20 probably means over 20 years) - If he had an accident during those 23 years, he paid the repair costs himself to avoid losing his "Schadensfreiheitsrabatt", his "no claim bonus / discount", these names seem to be used in Asia and Australia. -

The Canadian and Texas phrase seems to be:

"discounts or rebates for claim-free driving" -

http://psyc.queensu.ca/target/chapter11.html -

http://www.txcuins.com/auto/index.htm -

I have not found the British phrase yet, but my "Wörterbuch für alle Sparten der Versicherung" also shows "no-claim bonus". You can take your choice and add "... beginning of coverage" or "... basis year" or "... initial year" or "... policy issuance year" to translate "Rabattgrundjahr".