The stereo versions are new.
"Yakety Yak" is indeed in stereo, not mono.
With "Laurel & Hardy," there wasn't an existing stereo mix that Andrew Sandoval was comfortable with. He thought the four track needed to be re-synched with the eight track session for a better result . . . but they ran out of time.
Nevertheless, on the bonus version of "Laurel & Hardy" (with Jan's "la-la" vocal melody guide), you'll notice that the backing track is in stereo. If you really want to get a good idea of what's happening on "Laurel & Hardy," from an instrumental standpoint, that's the version to listen to. It's basically the de facto stereo version on this release.