Oddly, they only "officially" gave a Vanguard Satellite number of the ones that were successfully launched.
Two were attempted and failed before the third attempt made orbit, so then it was named Vanguard 1.
The next four failed, then the 8th one launched made orbit and was named Vanguard 2
Two more failed, then the 11th one attempted made orbit, and was named Vanguard 3
So, 3 out of 11, 27.3% success rate.
https://en.wikipedia.org/wiki/Vanguard_(rocket)#Launches
By comparison, Juno-I, which was the name given to the Jupiter-C rocket that launched the Explorer satellite, launched 6, three of which (#1, #3, and #4) made orbit (the failures all involved the upper stages in some manner , after booster burnout).
And those satellites were named Explorer 1 thru 6, regardless of whether they made orbit or not.
https://en.wikipedia.org/wiki/Juno_I#History
