According to Captain Eathan Pinnell Company "D" Mitchell's 8th Missouri Infantry in Banasik's book "Serving with Honor" page 75, Gen. Holmes and Gen. Frost were at Fort Pleasant and inspected the troops there on June 11th, the day before Clark's men left the next morning a 8 am to go to Napolean, Ark. June 12, 1863.

I am sure that Gen's Holmes, Frost and Col Clark would have discussed the upcoming operations of the next day. And I would assume(?) that special orders (if any) would have been verbally given at that time. This inspection trip could well have been a cover for such orders, since according to Pinnell, Clark's departure was delayed a day for this inspection. Or at least they delayed a day from their expected departure and all of a sudden Gens. Holmes and Frost show up to inspect the troops.

Would this be just coincidental?

In any case it would be normal military protocol for the commanding general (Holmes) to authorize any such expedition anyway no matter what the objectives were. Gen. Frost certain would not have acted independant of Holmes in ordering such an operation.