Yes they would be as silly as it seems. The rule also says "Any unit may use the Open Ground entrance benefits of a Vehicular-Sized Entrance—but only when entering it from outside that Factory....." this part of the rule seems to say you pay 1/4 movement and check bog anyway so it's essentially not a VSE just a rooftop access point.
Actually we have two parts to the rule.
1) A
fully-tracked AFV already within a Factory hex may move inside the same building at one-fourth (FRU) of its MP allotment per hex but must take a Bog Check with a +1 Factory DRM for each such hex entered, and to exit the building must pay normal building entrance costs (23.41) (expended in the building) and check for Bog/rubble prior to entering the non-factory hex.
So, you can move inside a building using 1/4 MP and take a Bog Check, and must pay normal building entry costs when you exit the building.
But, we have an exception to this statement...
2) [EXC: Any vehicle may enter/exit a Factory hex containing a printed stairwell symbol or across a road hexside at Open Ground costs provided the hex is controlled by friendly forces (the stairwell symbol in this case representing a vehicular-sized entrance)].
So, applying the exception to statement #1, we see that for a vehicle, there is no limitation as far as entering/exiting the building, just entering/exiting a Factory Hex as long as you are entering/exiting a stairwell symbol or across a road hexside.
It is after this that we get the statement you have quoted.
3) Any unit may use the Open Ground entrance benefits of a Vehicular Sized-Entrance - but only when entering it from outside that Factory and not if that Entrance is Roofless (see O5.42 for RED BARRICADES).
So, it appears that vehicles may use a VSE regardless of entering for outside the factory. I think this is pretty clear, since if you take statement #3 as overiding statement #2, and limiting VSE benefits to just entering from outside the factory, then vehicles which leave a factory via a VSE would not get Open Ground benefits and would need to pay full building entry costs and check for Bog/Rubble per statement #1.
Statement #3 allows non-vehicles to use Open Ground benefits, since Statement #2 already allows vehicles this benefit. The difference is statement #3 does not mention exiting since only fully-tracked AFV would need to pay exit costs (per statement #1) if they were not using a VSE (and other vehicles could not leave a factory through a non-VSE) and statement #2 already covers exiting a VSE for vehicles.
Effectively statement #3 adds the open ground benefit to all non-vehicles when entering from outside a factory.
Also note that Statement #2 allows all vehicles to enter/exit a factory through a VSE, and you can move fully-tracked AFV inside factory hexes that are not VSE (statement #1)
Bottom line is, if you assume stairwells are VSE in RB, then an interior stairwell hex would cost a vehicle Open Ground costs to enter, and would cost any other unit normal factory costs (since it is not entering from outside the factory). You can either interpret the rule that way, and use the entire rule, or you can interpret it to be VSE are just Road entry hexes in RB.
My 2 cents are on VSE as only Road entry hexes.
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