It's odd that his website - which is http://www.ralphmctell.co.uk/ - says he is celebrating 30 years on the road, as it also says his debut album was in 1968. Did he not tour until 1976, or become a full-time pro until then?
Possibly, instead, it is an example - and I have done it myself - of failing to realise quite how old one is/how much time has passed, and accidentally dropping a decade. Space Shuttle Challenger blowing up on launch and Olof Palme being assassinated in Sweden - was that 20 years ago or ten? (20).