Hi, thanks for your comment!

A generic =yes is set if there is no information about the parking position in the original tags. The old scheme would expect something like 
parking:lane:left=parallel  parking:lane:left:parallel=on_street
to be complete, where =on_street would convert to =lane

Unfortunately, many streets only provide orientation information and no information on the parking position. So a generic "yes" must be set to show that you _can_ park here, but there is no data about in what position.

Feel free to join the discussion for this organized editing effort at https://community.openstreetmap.org/t/organized-mapping-maproulette-challenge-convert-old-street-parking-tags-to-new-scheme/129253

Best,
Wieland