Fords of Isen Battles Puzzles

I'm puzzled about two items about these battles from the account in Unfinished Tales:

1) In the First Battle: a battalion of Uruks drive Theodred's defeated riders south down the river. The Riders make a stand against them on a hill. Then a horn sounds and the enemy disappears. The last sentence says:

"It was not till later that they discovered whither the Uruks had gone."

Where had they gone?

2) In the Second Battle: Erkenbrand sets out from Helm's Deep after errand-riders from Elfhelm inform him of the defeat at the Fords.

I still cannot envisage where he went. How did he gather the scattered riders without encountering the huge invasion of Isengarders advancing on Helm's Deep from the Fords and from the east side of the river?

[radagastly]

Well, of course, I don't have my books handy to check the timing, but as to the first question, mightn't these be the same Uruks sent to the Anduin to intercept the Fellowship and capture the Ring, if possible? I doubt if it says so, one way or the other, anywhere, but it seems right to me.

It's been a few years since I read that part, however . . .

[Rumil]

Hi Val and Rada,

on the missing Uruk Hai, they could possibly be Mauhur's lads who tried to relieve Ugluk by charging from the concealment of the forest towards Eomer's force, but were easily dealt with. Looking at the timings they couldn't be Ugluk's unit.

see here for some discussion
1st Battle of Isen on this page

I've also been a bit confused by Erkenbrand, as far as I can see he was not at either of the Battles of Isen, but was supposed to be in a position of command at the second battle. I guess its possible that he was trying to get to the Fords alone or with a few retainers when the invasion was going on, so must have had to detour to avoid Sarmuan's army.