For some inexplicable reason, the bill set Veterans Day commemorations for the fourth Monday of every October.
On Oct. 25, 1971, the first Veterans Day under this new bill was held. We’re not sure why it took three years to implement, but not surprisingly, there was a lot of confusion about the change, and many states were unhappy, choosing to continue to recognize the day as they previously had — in November.

Within a few years, it became pretty apparent that most U.S. citizens wanted to celebrate Veterans Day on Nov. 11, since it was a matter of historic and patriotic significance. So on Sept. 20, 1975, President Gerald Ford signed another law (Public Law 94-97), which returned the annual observance to its original date starting in 1978.
Source: History.com