As @ash says (multiple John Smiths) plus your particular John Smith might be represented by more than one ID. I think there may be different IDs for different combinations of name / age / address.
Examples (BTW I don’t have proof that any of the following are identical but I’m pretty sure! You be the judge):
Lance AIKMAN GREEN
https://beta.companieshouse.gov.uk/officers/p7q8j67Tb279vRIqO3sXgdo6K3U/appointments
Lance AIKMAN GREEN
https://beta.companieshouse.gov.uk/officers/RP0vk9IdLogXNHUkhPxqZaLJZ7E/appointments
(These two have the same name, age and address but the addresses differ by a comma).
Dominic Joseph Andrew CHAPPELL Born November 1966. There are several different IDs, and possibly one under Dominic CHAPPELL Born November 1966. Try searching Dominic CHAPPELL).
The scope / consistency of officer IDs seems to be a serially unanswered question.
An example with useful analysis:
http://forum.aws.chdev.org/t/how-is-officer-id-scoped/935
It’s the same but more so with PSC IDs (if you’re interested in those) - they don’t seem to be transferrable anywhere:
http://forum.aws.chdev.org/t/using-psc-id-in-api/648