Royal shield came in Market back in 2004-5. It was polymer protection they used to say 3 years but in reality it was just 6 months of protection, because if back in 2005 RS was giving you 3-5 years of protection then by today’s standards a single coat of Nano/Glass coat should give you 10-12 years of protection.
For all the practical reasons nothing on the market can protect your car for more than a year, you need to reapply what ever protection after some time.
As for RS I got it done too back in 2005 I kept my car for 7 years and the paint was in tip-top condition. I resently saw my old car and to be honest paint was still shining today (assuming the owner didn’t get it re-sprayed since then).
My car was always garage kept away from sunlight, acid rain, never driven in rain, always dust blown off first with a high power leaf blower then cleaned with running water using pressure washer then dried with high pressure air to clean all water from all the corners and then wipe cleaned with Meguiar quick detailed.