=SI(B2="";"";NBVAL(B$2:B2))
=SIERREUR(INDEX($C$2:C2;EQUIV(B3;$B$2:B2;0));MAX($C$2:C2)+1)
=SI(NB.SI($B$1:B1;$B2)>0;INDIRECT("C"&EQUIV($B2;$B:$B;0));MAX($C$1:$C1)+1)
=SI(B2="";"";1)
=SI(B3="";"";SI(ESTNA(EQUIV(B3;B$2:B2;0));1+MAX(C$2:C2);INDEX(C$2:C2;EQUIV(B3;B$2:B2;0))))