Thank you John
I ran a little test on a made up tree. All I added were parents A & B and a daughter C. I then added a husband and entered a marriage date.
A "1" was showing against the daughter and the new husband.
I then highlighted the husband and used the People drop-down feature selecting Detach. The tree display then just showed the husband as expected. I focused to the daughter and took out the marriage date but the "1" still appears next to her name. This confused me a little and maybe I have mis-understood something. I deleted the husband as well but the "1" remained.