Col wrote...
....
An example formula is;

=IF(AND($L$2-1=Main!I2,Main!I2=$L$2-7),"Anne",
""&IF(AND($L$2-1=Main!J2,Main!J2=$L$2-7),"Phil",
""&IF(AND($L$2-1=Main!K2,Main!K2=$L$2-7),"Gary",
""&IF(AND($L$2-1=Main!L2,Main!L2=$L$2-7),"Sandra",
""&IF(AND($L$2-1=Main!F2,Main!F2=$L$2-7),"John",
""&IF(AND($L$2-1=Main!N2,Main!N2=$L$2-7),"Alec",
""&IF(AND($L$2-1=Main!O2,Main!O2=$L$2-7),"Louise"," ")))))))
....

This formula can only show one name. It looks like you're missing right
parentheses. I believe you want

=TRIM(IF(AND($L$2-1=Main!I2,Main!I2=$L$2-7),"Anne"," ")
&IF(AND($L$2-1=Main!J2,Main!J2=$L$2-7),"Phil"," ")
&IF(AND($L$2-1=Main!K2,Main!K2=$L$2-7),"Gary"," ")
&IF(AND($L$2-1=Main!L2,Main!L2=$L$2-7),"Sandra"," ")
&IF(AND($L$2-1=Main!F2,Main!F2=$L$2-7),"John"," ")
&IF(AND($L$2-1=Main!N2,Main!N2=$L$2-7),"Alec"," ")
&IF(AND($L$2-1=Main!O2,Main!O2=$L$2-7),"Louise"," "))

One question: all the other names correspond to a progression from
Main!I2 through Main!O2 except John, which refers to Main!F2 rather
than Main!M2. Is that correct?