If a person who was born in the Avon area is located in another area through an event such as marriage, death, or counted in a census, their details may have been submitted for inclusion in the Strays Index.
In my article in the June Journal, I wrote about problems with the new FamilySearch database, where some Bristol events had been attributed to Abbots Leigh parish when they had in fact taken place elsewhere. This error now appears to have been corrected, and certainly some events that I checked are now shown as being at the right parish.
The big news for local researchers is the addition of over half a million Bristol parish records to FamilySearch. These cover Church of England parishes from 1837 onwards, and you may find BMD entries as late as the 1930s.