The cross country requirements laid down in FAR 61.129 are typically done before commencing a Part 61 Commercial. Notice that it refers to "ONE" flight. I therefore interpret that to mean one continuous flight with only the intermediate landings and no overnight stop. It makes no mention to not being able to carry passengers etc.
Not to unnecessarily cherry-pick your statement here, but the current 14 CFR 61.129 language regarding Commercial (airplane, single-engine land) reads:
(4) Ten hours of solo flight time in a single engine airplane or 10 hours of flight time performing the duties of pilot in command in a single engine airplane with an authorized instructor on board (either of which may be credited towards the flight time requirement under paragraph (a)(2) of this section), on the areas of operation listed under §61.127(b)(1) that include—
(i) One cross-country flight of not less than 300 nautical miles total distance...
Any old cross country time won't do for that. It MUST be performed either solo (meaning, no passengers), or with an authorized instructor on board. (This language is similar to that of the commercial MEL requirements now - the amendment adding "authorized instructor" was effective October, 2009.)