Scivillage.com Casual Discussion Science Forum

There are 21 active Falcon boosters after the expenditure of B1051 on its 14th flight. There are two more in the fleet that have completed 14 flights (B1058 and B1060). There are currently six unflown boosters in the fleet, of which five appear to be Falcon Heavy variants, which only leaves one fresh new conventional Falcon 9. (They have already proven the ability with B1052 to convert FH variants to regular satellite launchers.)

Of the 13 conventional Falcon 9's in the fleet...

1 has 0 flights
1 has 1 flight
1 has 3 flights
1 has 4 flights
1 has 5 flights
2 have 7 flights
1 has 8 flights
3 have 10 flights
2 have 14 flights

(Graphic by @_rykllan)