According to Colin Jose's NASL book Tony Macken was playing for Dallas Tornado and Washington Diplomats in 1977 at the same time! I guess his appearances before July 21rd for Dallas belong to another player. Can someone solve this problem?

1976 + 1977 Washington Diplomats
1977 Dallas Tornados

I know, according to the book he played 15 matches 1 goal for Washington and 10 matches 1 goal for Dallas in 1977, but this can't be correct. This would mean he played for 2 teams between June 18th-July 16th. I need to know exact date of his transfer and to which other player belong these appearances. I found somewhere in July.