Previous reviewers are correct:
1. This IS the third series that appeared on TV, but
2. On the original boxed set is is clearly described as series 1.
It appears that virtually no KNOWN copies exist of any episodes from the first two televised series. So I guess there's little chance we'll ever get to see them now.
Which is unfortunate since they were IMO a lot more raw and gutsy than the later series, possibly helped by the fact that they were in black and white rather than in colour.
FWIW, Callan's original name was "John Craig" - a sort of poor man's James Bond and a close relation of Len Deighton's "Harry Palmer" in "The Ipcress File" which had come out a year or two earlier. James Mitchell, using the name James Munro, created the Craig character in a series of four (?) books, which also featured "Lonely". In the Craig stories Lonely was a "ton-up boy" (a biker), though he smelled awful even then. "Mind Bender" Snell was also in the books, though under a different name, if I remember correctly. And Mitchell occasionally recycled whole incidents. The storyline about the gun dealer in "Callan - the Movie", for example, was originally in one of the Craig books.
Callan was in turn a poor man's version of John Craig, though much of Craig's basic character carried over from the books into the TV episodes. Ronald Radd as Hunter was IMO the perfect realization of Craig's boss in the books.