Yellow Line - where does it go?

Just got back from E Street (saw The Flight of the Red Balloon, pretty interesting). I noticed something on the Metro map I hadn't focused on before, not being a Yellow Line rider.

First, the Yellow Line starts at Fort Totten, basically duplicates the Green to L'Enfant Plaza, where it cuts away, runs under the Potomac, and joins the Blue at Pentagon, cutting off again at King Street and running by itself for two stops to Huntington (see the map). On the map are two service notes, one quite clear and the other... not.

• Every other outbound Red Line train terminates at Grosvenor-Strathmore Station on weekdays from 7:00-9:30AM and 4:00-6:30PM.
• Yellow Line service operates between Mt. Vernon Sq/7th St-Convention Center and Fort Totten stations EXCEPT on weekdays from 5:00-9:30AM and 3:00-7:00PM.

Okay. Where does the Yellow Line go during weekday rush?

Does it go from Huntington to Fort Totten (that is, the whole route)? That would be a reading of "ONLY between Mt Vernon and Fort Totten EXCEPT during rush". Or from Huntington to Mt. Vernon Square (that is, NOT from Mt. Vernon Square to Fort Totten)? That would be the reading of "NOT between Mt Vernon and Fort Totten during rush".

Pragmatics suggests it runs the whole route during rush hour. But then again, pragmatics suggests it would be odd to have no service at all from Huntington on the weekends. So, honestly, this sign doesn't help me at all.

If you're wondering, the actual answer is that the Yellow Line operates from Huntington to Fort Totten on weekends and weekday mid-days and nights. It stops at Mt Vernon Square during the rush, leaving the tracks for more, and more frequent, Green Line trains. So Yellow Line riders must transfer at Mt Vernon Square if they want to go to Fort Totten during the rush.

And yes, that reading is allowed by the sign. But it's not the only one. Why can't the notice be as clear as the Red Line one?

• Yellow Line service does not operate between Mt. Vernon Sq/7th St-Convention Center and Fort Totten stations on weekdays from 5:00-9:30AM and 3:00-7:00PM.