wrong date? (not sure if I picked the correct component, btw)

The problem is the javascript output only. The php is correct.

The problem is the in nodeadmin.js on line 62:

      dateString = dateChanged.getFullYear() + '/' + padNumber(dateChanged.getMonth() , 2) + '/' + padNumber(dateChanged.getDate(), 2) + ' - ' + padNumber(dateChanged.getHours(), 2) + ':' + padNumber(dateChanged.getMinutes(), 2);

The problem is that javascript's .getMonth command believes January to be 0, not 1.
There are two remedies.

1. Add 1 to the value returned: ... padNumber((dateChanged.getMonth() +1) , 2) ...
2. Make an array function in the javascript that returns the correct month (usually this is used for getting the name of the month).
   Psuedo code:

   function getMonthName(number){
   var month=new Array(12);
    month[0]="January";
    month[1]="February";
    month[2]="March";
    month[3]="April";
    month[4]="May";
    month[5]="June";
    month[6]="July";
    month[7]="August";
    month[8]="September";
    month[9]="October";
    month[10]="November";
    month[11]="December";
    return month[number];
   }
   

Personally, I'm going to adopt the first. It's faster, and we don't need the names. But I'll leave that up to Detour's next release.

Detour, just a thought, but maybe it would better if you left the date parsing out of the javascript entirely?
Having it format the date server side would keep things accurate, and allow others to modify if desired.

For simplicity, I'm going to define a global variable: NODE_ADMIN_DATE_FORMAT with your current custom date string. But it could easily be stored in a drupal_variable.
In nodeadmin.module around line 300, insert:

$results['nodeData'][$obj->nid]->formattedDate = format_date($obj->changed, 'custom', NODE_ADMIN_DATE_FORMAT);

Update line 130ish (sorry, I'm adding code so mine doesn't match yours exactly anymore) to:
'data' => $node->formattedDate,

In nodeadmin.js around line 61, remove:

dateChanged = new Date(nodeData[nid].changed * 1000);
dateString = dateChanged.getFullYear() + '/' + padNumber((dateChanged.getMonth() + 1), 2) + '/' + padNumber(dateChanged.getDate(), 2) + ' - ' + padNumber(dateChanged.getHours(), 2) + ':' + padNumber(dateChanged.getMinutes(), 2);

Update line 64ish to:
tableBody.append( ...

');

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