I went here today and couldn't find the trail leading from Innis Arden Reserve Park to Spring Beach. The only trail I saw is the one that leads from 15th Ave NW to 16th Ave NW.

Perhaps a trail exists, but wasn't visible due to overgrown vegetation. I'll try to make it out here in the winter to see if it's visible. If not, I plan to remove it.

The street sign at this intersection reads "N INNIS ARDEN WY". The street sign at the intersection with 6th Ave NW reads "NW INNIS ARDEN WY".

It's probably N Innis Arden Way to the east of 1st Ave NW and NW Innis Arden Way to the west of 1st Ave NW, assuming it follows the naming convention used elsewhere in North Seattle/Shoreline.

Strava heatmap suggests that there may be a trail through the woods here

Strava heatmap suggests there may be a path between the Snohomish County PUD right of way and Lynnwood HS through the woods here.

A 2.5 km segment of Bells Mountain Trail is marked as a bridge. I believe this may be a mistake. It doesn't look like a bridge on aerial imagery.

I added the bike lane on the west side of the road in osm.org/changeset/154529554, but I couldn't clearly see the the east side of the road in the video I took. Is bike lane on that side complete?

The plans for it are available here: https://seattle.gov/documents/Departments/SDOT/BikeProgram/EastlakeBike_InfoMap_20200106.pdf

This road is fenced off for construction.