Unsure.
NERC If you mean Natural Environment Research Council, I'm unclear as to the relevance.
What does NSG mean?
Can you tell me which OOC OS maps, or definitive statements shows these definitions.
By your own statement (& trail's) unclassified_highway appears to be a classification rather than a designation of a right of way.
As an example could you explain where you got the designation for way/42959405

Hi
The convention is to not add 'Rail Station' to railway=station name tags.

As it's only one entity just revert the tags .

Hi
What source informed you they are municipally maintained?

Hi
Are you sure? Has it been reopened?
Avon Valley Trail isn't the path's name. It's the name of just one route which can pass along the way. See the attached route relations.

Hi
What is a unclassified_highway designation?

Hi
FYI railway=station already exists. There mapped as nodes separate from building=train_station

Hi
Do you have local knowledge for these edits?
It's unclear from your ambiguous comment "I have fixed a mistake" Please be more detailed, here & when closing a note.

Hi
1a I've no idea if it's private
1b If you want to
2 If you want to
3 I didn't add those tags. I copied them from one way to another
4a If you want to
4b If you want to add a barrier, fine, but are you sure it requires one
5 Not convinced it's maintained grass, but if you want to.
6 If you want to.
7 If you want to
8 On Bing it's mostly bare earth & there's clearly livestock.
9a Rubbish.
9b If you want to.

Open, as in the area where the activities are performed are not obstructed.
the 'general recreation' has no implication of ownership. Read the second sentence.

Have a read of leisure=pitch

As can be seen in aerial imagery the Triangle Field has multiple pitches which should be mapped individually.

Hi
Welcome to OSM
Could you provide more detailed changeset comments than 'more information on area'. It helps those of us who validate amendments.

way/405862099
amenity is the correct tag for a school boundary. building-school goes on the individual building within the school

Same point here

Hi
Cricket pitches aren't square & don't include a pavilion. This is a recreation ground.

Hi
Welcome to OSM
Could you provide a more descriptive changeset comment than "made changes"? Something like 'NCN 4 route amended due to...'
You've created a separate cycleway:
osm.org
/way/680909013
Is the route not shared path at this point?
It's created a gap in the route which requires fixing:
http://ra.osmsurround.org/analyzeMap?relationId=1318929
Is there a reason the route can't continue on the pavement to the West of Chelsea Bridge until it reaches one of the pedestrian crossings?

This section should be part of relation/1318928
You've added it to the super relation/1318931 which should only contain other relations.

What proof have you that there are toilets other than disabled at the locations you've amended?
You didn't conclude the discussion on this subject on Talk:GB.

Hi What were you attempt to achieve with this changeset?
This was removed:
way/600468563

Same Q as before.

Hi
What landuse is it? Yes isn't detailed enough.

What are these?
way/650647038